Enable @typescript-eslint/explicit-function-return-type in /src (#9788)

* Enable `@typescript-eslint/explicit-member-accessibility` on /src

* Prettier

* Enable `@typescript-eslint/explicit-function-return-type` in /src

* Fix types

* tsc strict fixes

* Delint

* Fix test

* Fix bad merge

.eslintrc.js

@@ -100,8 +100,12 @@ module.exports = {
             files: ["src/**/*.{ts,tsx}", "test/**/*.{ts,tsx}", "cypress/**/*.ts"],
             extends: ["plugin:matrix-org/typescript", "plugin:matrix-org/react"],
             rules: {
-                // temporary disabled
-                "@typescript-eslint/explicit-function-return-type": "off",
+                "@typescript-eslint/explicit-function-return-type": [
+                    "error",
+                    {
+                        allowExpressions: true,
+                    },
+                ],
 
                 // Things we do that break the ideal style
                 "prefer-promise-reject-errors": "off",

src/@types/diff-dom.d.ts

@@ -20,10 +20,10 @@ declare module "diff-dom" {
         name: string;
         text?: string;
         route: number[];
-        value: string;
-        element: unknown;
-        oldValue: string;
-        newValue: string;
+        value: HTMLElement | string;
+        element: HTMLElement | string;
+        oldValue: HTMLElement | string;
+        newValue: HTMLElement | string;
     }
 
     interface IOpts {}

src/@types/polyfill.ts

@@ -15,7 +15,7 @@ limitations under the License.
 */
 
 // This is intended to fix re-resizer because of its unguarded `instanceof TouchEvent` checks.
-export function polyfillTouchEvent() {
+export function polyfillTouchEvent(): void {
     // Firefox doesn't have touch events without touch devices being present, so create a fake
     // one we can rely on lying about.
     if (!window.TouchEvent) {

src/AsyncWrapper.tsx

@@ -47,7 +47,7 @@ export default class AsyncWrapper extends React.Component<IProps, IState> {
         error: null,
     };
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         // XXX: temporary logging to try to diagnose
         // https://github.com/vector-im/element-web/issues/3148
         logger.log("Starting load of AsyncWrapper for modal");
@@ -69,15 +69,15 @@ export default class AsyncWrapper extends React.Component<IProps, IState> {
             });
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         this.unmounted = true;
     }
 
-    private onWrapperCancelClick = () => {
+    private onWrapperCancelClick = (): void => {
         this.props.onFinished(false);
     };
 
-    public render() {
+    public render(): JSX.Element {
         if (this.state.component) {
             const Component = this.state.component;
             return <Component {...this.props} />;

src/Avatar.ts

@@ -137,7 +137,12 @@ export function getInitialLetter(name: string): string {
     return split(name, "", 1)[0].toUpperCase();
 }
 
-export function avatarUrlForRoom(room: Room, width: number, height: number, resizeMethod?: ResizeMethod) {
+export function avatarUrlForRoom(
+    room: Room,
+    width: number,
+    height: number,
+    resizeMethod?: ResizeMethod,
+): string | null {
     if (!room) return null; // null-guard
 
     if (room.getMxcAvatarUrl()) {

src/BasePlatform.ts

@@ -272,7 +272,7 @@ export default abstract class BasePlatform {
         return null;
     }
 
-    public setLanguage(preferredLangs: string[]) {}
+    public setLanguage(preferredLangs: string[]): void {}
 
     public setSpellCheckEnabled(enabled: boolean): void {}
 
@@ -280,7 +280,7 @@ export default abstract class BasePlatform {
         return null;
     }
 
-    public setSpellCheckLanguages(preferredLangs: string[]) {}
+    public setSpellCheckLanguages(preferredLangs: string[]): void {}
 
     public getSpellCheckLanguages(): Promise<string[]> | null {
         return null;

src/BlurhashEncoder.ts

@@ -40,7 +40,7 @@ export class BlurhashEncoder {
         this.worker.onmessage = this.onMessage;
     }
 
-    private onMessage = (ev: MessageEvent<IBlurhashWorkerResponse>) => {
+    private onMessage = (ev: MessageEvent<IBlurhashWorkerResponse>): void => {
         const { seq, blurhash } = ev.data;
         const deferred = this.pendingDeferredMap.get(seq);
         if (deferred) {

src/ContentMessages.ts

@@ -68,16 +68,20 @@ interface IMediaConfig {
  * @param {File} imageFile The file to load in an image element.
  * @return {Promise} A promise that resolves with the html image element.
  */
-async function loadImageElement(imageFile: File) {
+async function loadImageElement(imageFile: File): Promise<{
+    width: number;
+    height: number;
+    img: HTMLImageElement;
+}> {
     // Load the file into an html element
     const img = new Image();
     const objectUrl = URL.createObjectURL(imageFile);
     const imgPromise = new Promise((resolve, reject) => {
-        img.onload = function () {
+        img.onload = function (): void {
             URL.revokeObjectURL(objectUrl);
             resolve(img);
         };
-        img.onerror = function (e) {
+        img.onerror = function (e): void {
             reject(e);
         };
     });
@@ -185,13 +189,13 @@ function loadVideoElement(videoFile: File): Promise<HTMLVideoElement> {
 
         const reader = new FileReader();
 
-        reader.onload = function (ev) {
+        reader.onload = function (ev): void {
             // Wait until we have enough data to thumbnail the first frame.
-            video.onloadeddata = async function () {
+            video.onloadeddata = async function (): Promise<void> {
                 resolve(video);
                 video.pause();
             };
-            video.onerror = function (e) {
+            video.onerror = function (e): void {
                 reject(e);
             };
 
@@ -206,7 +210,7 @@ function loadVideoElement(videoFile: File): Promise<HTMLVideoElement> {
             video.load();
             video.play();
         };
-        reader.onerror = function (e) {
+        reader.onerror = function (e): void {
             reject(e);
         };
         reader.readAsDataURL(videoFile);
@@ -253,10 +257,10 @@ function infoForVideoFile(
 function readFileAsArrayBuffer(file: File | Blob): Promise<ArrayBuffer> {
     return new Promise((resolve, reject) => {
         const reader = new FileReader();
-        reader.onload = function (e) {
+        reader.onload = function (e): void {
             resolve(e.target.result as ArrayBuffer);
         };
-        reader.onerror = function (e) {
+        reader.onerror = function (e): void {
             reject(e);
         };
         reader.readAsArrayBuffer(file);
@@ -461,7 +465,7 @@ export default class ContentMessages {
         matrixClient: MatrixClient,
         replyToEvent: MatrixEvent | undefined,
         promBefore?: Promise<any>,
-    ) {
+    ): Promise<void> {
         const fileName = file.name || _t("Attachment");
         const content: Omit<IMediaEventContent, "info"> & { info: Partial<IMediaEventInfo> } = {
             body: fileName,
@@ -491,7 +495,7 @@ export default class ContentMessages {
         this.inprogress.push(upload);
         dis.dispatch<UploadStartedPayload>({ action: Action.UploadStarted, upload });
 
-        function onProgress(progress: UploadProgress) {
+        function onProgress(progress: UploadProgress): void {
             upload.onProgress(progress);
             dis.dispatch<UploadProgressPayload>({ action: Action.UploadProgress, upload });
         }
@@ -568,7 +572,7 @@ export default class ContentMessages {
         }
     }
 
-    private isFileSizeAcceptable(file: File) {
+    private isFileSizeAcceptable(file: File): boolean {
         if (
             this.mediaConfig !== null &&
             this.mediaConfig["m.upload.size"] !== undefined &&
@@ -599,7 +603,7 @@ export default class ContentMessages {
             });
     }
 
-    public static sharedInstance() {
+    public static sharedInstance(): ContentMessages {
         if (window.mxContentMessages === undefined) {
             window.mxContentMessages = new ContentMessages();
         }

src/DateUtils.ts

@@ -188,7 +188,7 @@ export function wantsDateSeparator(prevEventDate: Date, nextEventDate: Date): bo
     return prevEventDate.getDay() !== nextEventDate.getDay();
 }
 
-export function formatFullDateNoDay(date: Date) {
+export function formatFullDateNoDay(date: Date): string {
     return _t("%(date)s at %(time)s", {
         date: date.toLocaleDateString().replace(/\//g, "-"),
         time: date.toLocaleTimeString().replace(/:/g, "-"),
@@ -205,7 +205,7 @@ export function formatFullDateNoDayISO(date: Date): string {
     return date.toISOString();
 }
 
-export function formatFullDateNoDayNoTime(date: Date) {
+export function formatFullDateNoDayNoTime(date: Date): string {
     return date.getFullYear() + "/" + pad(date.getMonth() + 1) + "/" + pad(date.getDate());
 }
 

src/DeviceListener.ts

@@ -19,6 +19,7 @@ import { logger } from "matrix-js-sdk/src/logger";
 import { CryptoEvent } from "matrix-js-sdk/src/crypto";
 import { ClientEvent, EventType, RoomStateEvent } from "matrix-js-sdk/src/matrix";
 import { SyncState } from "matrix-js-sdk/src/sync";
+import { IKeyBackupInfo } from "matrix-js-sdk/src/crypto/keybackup";
 
 import { MatrixClientPeg } from "./MatrixClientPeg";
 import dis from "./dispatcher/dispatcher";
@@ -56,7 +57,7 @@ export default class DeviceListener {
     // has the user dismissed any of the various nag toasts to setup encryption on this device?
     private dismissedThisDeviceToast = false;
     // cache of the key backup info
-    private keyBackupInfo: object = null;
+    private keyBackupInfo: IKeyBackupInfo | null = null;
     private keyBackupFetchedAt: number = null;
     private keyBackupStatusChecked = false;
     // We keep a list of our own device IDs so we can batch ones that were already
@@ -70,12 +71,12 @@ export default class DeviceListener {
     private enableBulkUnverifiedSessionsReminder = true;
     private deviceClientInformationSettingWatcherRef: string | undefined;
 
-    public static sharedInstance() {
+    public static sharedInstance(): DeviceListener {
         if (!window.mxDeviceListener) window.mxDeviceListener = new DeviceListener();
         return window.mxDeviceListener;
     }
 
-    public start() {
+    public start(): void {
         this.running = true;
         MatrixClientPeg.get().on(CryptoEvent.WillUpdateDevices, this.onWillUpdateDevices);
         MatrixClientPeg.get().on(CryptoEvent.DevicesUpdated, this.onDevicesUpdated);
@@ -98,7 +99,7 @@ export default class DeviceListener {
         this.updateClientInformation();
     }
 
-    public stop() {
+    public stop(): void {
         this.running = false;
         if (MatrixClientPeg.get()) {
             MatrixClientPeg.get().removeListener(CryptoEvent.WillUpdateDevices, this.onWillUpdateDevices);
@@ -134,7 +135,7 @@ export default class DeviceListener {
      *
      * @param {String[]} deviceIds List of device IDs to dismiss notifications for
      */
-    public async dismissUnverifiedSessions(deviceIds: Iterable<string>) {
+    public async dismissUnverifiedSessions(deviceIds: Iterable<string>): Promise<void> {
         logger.log("Dismissing unverified sessions: " + Array.from(deviceIds).join(","));
         for (const d of deviceIds) {
             this.dismissed.add(d);
@@ -143,19 +144,19 @@ export default class DeviceListener {
         this.recheck();
     }
 
-    public dismissEncryptionSetup() {
+    public dismissEncryptionSetup(): void {
         this.dismissedThisDeviceToast = true;
         this.recheck();
     }
 
-    private ensureDeviceIdsAtStartPopulated() {
+    private ensureDeviceIdsAtStartPopulated(): void {
         if (this.ourDeviceIdsAtStart === null) {
             const cli = MatrixClientPeg.get();
             this.ourDeviceIdsAtStart = new Set(cli.getStoredDevicesForUser(cli.getUserId()).map((d) => d.deviceId));
         }
     }
 
-    private onWillUpdateDevices = async (users: string[], initialFetch?: boolean) => {
+    private onWillUpdateDevices = async (users: string[], initialFetch?: boolean): Promise<void> => {
         // If we didn't know about *any* devices before (ie. it's fresh login),
         // then they are all pre-existing devices, so ignore this and set the
         // devicesAtStart list to the devices that we see after the fetch.
@@ -168,26 +169,26 @@ export default class DeviceListener {
         // before we download any new ones.
     };
 
-    private onDevicesUpdated = (users: string[]) => {
+    private onDevicesUpdated = (users: string[]): void => {
         if (!users.includes(MatrixClientPeg.get().getUserId())) return;
         this.recheck();
     };
 
-    private onDeviceVerificationChanged = (userId: string) => {
+    private onDeviceVerificationChanged = (userId: string): void => {
         if (userId !== MatrixClientPeg.get().getUserId()) return;
         this.recheck();
     };
 
-    private onUserTrustStatusChanged = (userId: string) => {
+    private onUserTrustStatusChanged = (userId: string): void => {
         if (userId !== MatrixClientPeg.get().getUserId()) return;
         this.recheck();
     };
 
-    private onCrossSingingKeysChanged = () => {
+    private onCrossSingingKeysChanged = (): void => {
         this.recheck();
     };
 
-    private onAccountData = (ev: MatrixEvent) => {
+    private onAccountData = (ev: MatrixEvent): void => {
         // User may have:
         // * migrated SSSS to symmetric
         // * uploaded keys to secret storage
@@ -202,13 +203,13 @@ export default class DeviceListener {
         }
     };
 
-    private onSync = (state: SyncState, prevState?: SyncState) => {
+    private onSync = (state: SyncState, prevState?: SyncState): void => {
         if (state === "PREPARED" && prevState === null) {
             this.recheck();
         }
     };
 
-    private onRoomStateEvents = (ev: MatrixEvent) => {
+    private onRoomStateEvents = (ev: MatrixEvent): void => {
         if (ev.getType() !== EventType.RoomEncryption) return;
 
         // If a room changes to encrypted, re-check as it may be our first
@@ -216,7 +217,7 @@ export default class DeviceListener {
         this.recheck();
     };
 
-    private onAction = ({ action }: ActionPayload) => {
+    private onAction = ({ action }: ActionPayload): void => {
         if (action !== Action.OnLoggedIn) return;
         this.recheck();
         this.updateClientInformation();
@@ -224,7 +225,7 @@ export default class DeviceListener {
 
     // The server doesn't tell us when key backup is set up, so we poll
     // & cache the result
-    private async getKeyBackupInfo() {
+    private async getKeyBackupInfo(): Promise<IKeyBackupInfo> {
         const now = new Date().getTime();
         if (!this.keyBackupInfo || this.keyBackupFetchedAt < now - KEY_BACKUP_POLL_INTERVAL) {
             this.keyBackupInfo = await MatrixClientPeg.get().getKeyBackupVersion();
@@ -233,7 +234,7 @@ export default class DeviceListener {
         return this.keyBackupInfo;
     }
 
-    private shouldShowSetupEncryptionToast() {
+    private shouldShowSetupEncryptionToast(): boolean {
         // If we're in the middle of a secret storage operation, we're likely
         // modifying the state involved here, so don't add new toasts to setup.
         if (isSecretStorageBeingAccessed()) return false;
@@ -242,7 +243,7 @@ export default class DeviceListener {
         return cli && cli.getRooms().some((r) => cli.isRoomEncrypted(r.roomId));
     }
 
-    private async recheck() {
+    private async recheck(): Promise<void> {
         if (!this.running) return; // we have been stopped
         const cli = MatrixClientPeg.get();
 
@@ -359,7 +360,7 @@ export default class DeviceListener {
         this.displayingToastsForDeviceIds = newUnverifiedDeviceIds;
     }
 
-    private checkKeyBackupStatus = async () => {
+    private checkKeyBackupStatus = async (): Promise<void> => {
         if (this.keyBackupStatusChecked) {
             return;
         }
@@ -388,7 +389,7 @@ export default class DeviceListener {
         }
     };
 
-    private updateClientInformation = async () => {
+    private updateClientInformation = async (): Promise<void> => {
         try {
             if (this.shouldRecordClientInformation) {
                 await recordClientInformation(MatrixClientPeg.get(), SdkConfig.get(), PlatformPeg.get());

src/Editing.ts

@@ -16,5 +16,6 @@ limitations under the License.
 
 import { TimelineRenderingType } from "./contexts/RoomContext";
 
-export const editorRoomKey = (roomId: string, context: TimelineRenderingType) => `mx_edit_room_${roomId}_${context}`;
-export const editorStateKey = (eventId: string) => `mx_edit_state_${eventId}`;
+export const editorRoomKey = (roomId: string, context: TimelineRenderingType): string =>
+    `mx_edit_room_${roomId}_${context}`;
+export const editorStateKey = (eventId: string): string => `mx_edit_state_${eventId}`;

src/HtmlUtils.tsx

@@ -449,9 +449,9 @@ export interface IOptsReturnString extends IOpts {
     returnString: true;
 }
 
-const emojiToHtmlSpan = (emoji: string) =>
+const emojiToHtmlSpan = (emoji: string): string =>
     `<span class='mx_Emoji' title='${unicodeToShortcode(emoji)}'>${emoji}</span>`;
-const emojiToJsxSpan = (emoji: string, key: number) => (
+const emojiToJsxSpan = (emoji: string, key: number): JSX.Element => (
     <span key={key} className="mx_Emoji" title={unicodeToShortcode(emoji)}>
         {emoji}
     </span>
@@ -505,7 +505,7 @@ function formatEmojis(message: string, isHtmlMessage: boolean): (JSX.Element | s
  */
 export function bodyToHtml(content: IContent, highlights: Optional<string[]>, opts: IOptsReturnString): string;
 export function bodyToHtml(content: IContent, highlights: Optional<string[]>, opts: IOptsReturnNode): ReactNode;
-export function bodyToHtml(content: IContent, highlights: Optional<string[]>, opts: IOpts = {}) {
+export function bodyToHtml(content: IContent, highlights: Optional<string[]>, opts: IOpts = {}): ReactNode | string {
     const isFormattedBody = content.format === "org.matrix.custom.html" && !!content.formatted_body;
     let bodyHasEmoji = false;
     let isHtmlMessage = false;

src/ImageUtils.ts

@@ -28,7 +28,7 @@ limitations under the License.
  * consume in the timeline, when performing scroll offset calculations
  * (e.g. scroll locking)
  */
-export function thumbHeight(fullWidth: number, fullHeight: number, thumbWidth: number, thumbHeight: number) {
+export function thumbHeight(fullWidth: number, fullHeight: number, thumbWidth: number, thumbHeight: number): number {
     if (!fullWidth || !fullHeight) {
         // Cannot calculate thumbnail height for image: missing w/h in metadata. We can't even
         // log this because it's spammy

src/Keyboard.ts

@@ -76,7 +76,7 @@ export const Key = {
 
 export const IS_MAC = navigator.platform.toUpperCase().includes("MAC");
 
-export function isOnlyCtrlOrCmdKeyEvent(ev) {
+export function isOnlyCtrlOrCmdKeyEvent(ev: KeyboardEvent): boolean {
     if (IS_MAC) {
         return ev.metaKey && !ev.altKey && !ev.ctrlKey && !ev.shiftKey;
     } else {

src/LegacyCallHandler.tsx

@@ -169,7 +169,7 @@ export default class LegacyCallHandler extends EventEmitter {
 
     private silencedCalls = new Set<string>(); // callIds
 
-    public static get instance() {
+    public static get instance(): LegacyCallHandler {
         if (!window.mxLegacyCallHandler) {
             window.mxLegacyCallHandler = new LegacyCallHandler();
         }
@@ -456,7 +456,7 @@ export default class LegacyCallHandler extends EventEmitter {
         return callsNotInThatRoom;
     }
 
-    public getAllActiveCallsForPip(roomId: string) {
+    public getAllActiveCallsForPip(roomId: string): MatrixCall[] {
         const room = MatrixClientPeg.get().getRoom(roomId);
         if (WidgetLayoutStore.instance.hasMaximisedWidget(room)) {
             // This checks if there is space for the call view in the aux panel
@@ -478,7 +478,7 @@ export default class LegacyCallHandler extends EventEmitter {
         const audio = document.getElementById(audioId) as HTMLMediaElement;
         if (audio) {
             this.addEventListenersForAudioElement(audio);
-            const playAudio = async () => {
+            const playAudio = async (): Promise<void> => {
                 try {
                     if (audio.muted) {
                         logger.error(
@@ -524,7 +524,7 @@ export default class LegacyCallHandler extends EventEmitter {
         // TODO: Attach an invisible element for this instead
         // which listens?
         const audio = document.getElementById(audioId) as HTMLMediaElement;
-        const pauseAudio = () => {
+        const pauseAudio = (): void => {
             logger.debug(`${logPrefix} pausing audio`);
             // pause doesn't return a promise, so just do it
             audio.pause();
@@ -600,7 +600,7 @@ export default class LegacyCallHandler extends EventEmitter {
             this.setCallListeners(newCall);
             this.setCallState(newCall, newCall.state);
         });
-        call.on(CallEvent.AssertedIdentityChanged, async () => {
+        call.on(CallEvent.AssertedIdentityChanged, async (): Promise<void> => {
             if (!this.matchesCallForThisRoom(call)) return;
 
             logger.log(`Call ID ${call.callId} got new asserted identity:`, call.getRemoteAssertedIdentity());
@@ -808,7 +808,7 @@ export default class LegacyCallHandler extends EventEmitter {
 
     private showICEFallbackPrompt(): void {
         const cli = MatrixClientPeg.get();
-        const code = (sub) => <code>{sub}</code>;
+        const code = (sub: string): JSX.Element => <code>{sub}</code>;
         Modal.createDialog(
             QuestionDialog,
             {

src/Lifecycle.ts

@@ -219,7 +219,7 @@ export function attemptTokenLogin(
     })
         .then(function (creds) {
             logger.log("Logged in with token");
-            return clearStorage().then(async () => {
+            return clearStorage().then(async (): Promise<boolean> => {
                 await persistCredentials(creds);
                 // remember that we just logged in
                 sessionStorage.setItem("mx_fresh_login", String(true));
@@ -406,7 +406,7 @@ async function pickleKeyToAesKey(pickleKey: string): Promise<Uint8Array> {
     );
 }
 
-async function abortLogin() {
+async function abortLogin(): Promise<void> {
     const signOut = await showStorageEvictedDialog();
     if (signOut) {
         await clearStorage();

src/Livestream.ts

@@ -20,14 +20,14 @@ import { MatrixClientPeg } from "./MatrixClientPeg";
 import SdkConfig from "./SdkConfig";
 import { ElementWidgetActions } from "./stores/widgets/ElementWidgetActions";
 
-export function getConfigLivestreamUrl() {
+export function getConfigLivestreamUrl(): string | undefined {
     return SdkConfig.get("audio_stream_url");
 }
 
 // Dummy rtmp URL used to signal that we want a special audio-only stream
 const AUDIOSTREAM_DUMMY_URL = "rtmp://audiostream.dummy/";
 
-async function createLiveStream(roomId: string) {
+async function createLiveStream(roomId: string): Promise<void> {
     const openIdToken = await MatrixClientPeg.get().getOpenIdToken();
 
     const url = getConfigLivestreamUrl() + "/createStream";
@@ -47,7 +47,7 @@ async function createLiveStream(roomId: string) {
     return respBody["stream_id"];
 }
 
-export async function startJitsiAudioLivestream(widgetMessaging: ClientWidgetApi, roomId: string) {
+export async function startJitsiAudioLivestream(widgetMessaging: ClientWidgetApi, roomId: string): Promise<void> {
     const streamId = await createLiveStream(roomId);
 
     await widgetMessaging.transport.send(ElementWidgetActions.StartLiveStream, {

src/Login.ts

@@ -122,7 +122,7 @@ export default class Login {
             initial_device_display_name: this.defaultDeviceDisplayName,
         };
 
-        const tryFallbackHs = (originalError) => {
+        const tryFallbackHs = (originalError: Error): Promise<IMatrixClientCreds> => {
             return sendLoginRequest(this.fallbackHsUrl, this.isUrl, "m.login.password", loginParams).catch(
                 (fallbackError) => {
                     logger.log("fallback HS login failed", fallbackError);

src/Markdown.ts

@@ -56,7 +56,7 @@ function isMultiLine(node: commonmark.Node): boolean {
     return par.firstChild != par.lastChild;
 }
 
-function getTextUntilEndOrLinebreak(node: commonmark.Node) {
+function getTextUntilEndOrLinebreak(node: commonmark.Node): string {
     let currentNode = node;
     let text = "";
     while (currentNode !== null && currentNode.type !== "softbreak" && currentNode.type !== "linebreak") {
@@ -137,7 +137,7 @@ export default class Markdown {
      * See: https://github.com/vector-im/element-web/issues/4674
      * @param parsed
      */
-    private repairLinks(parsed: commonmark.Node) {
+    private repairLinks(parsed: commonmark.Node): commonmark.Node {
         const walker = parsed.walker();
         let event: commonmark.NodeWalkingStep = null;
         let text = "";

src/Modal.tsx

@@ -77,7 +77,7 @@ export class ModalManager extends TypedEventEmitter<ModalManagerEvent, HandlerMa
     // Neither the static nor priority modal will be in this list.
     private modals: IModal<any>[] = [];
 
-    private static getOrCreateContainer() {
+    private static getOrCreateContainer(): HTMLElement {
         let container = document.getElementById(DIALOG_CONTAINER_ID);
 
         if (!container) {
@@ -89,7 +89,7 @@ export class ModalManager extends TypedEventEmitter<ModalManagerEvent, HandlerMa
         return container;
     }
 
-    private static getOrCreateStaticContainer() {
+    private static getOrCreateStaticContainer(): HTMLElement {
         let container = document.getElementById(STATIC_DIALOG_CONTAINER_ID);
 
         if (!container) {
@@ -101,31 +101,31 @@ export class ModalManager extends TypedEventEmitter<ModalManagerEvent, HandlerMa
         return container;
     }
 
-    public toggleCurrentDialogVisibility() {
+    public toggleCurrentDialogVisibility(): void {
         const modal = this.getCurrentModal();
         if (!modal) return;
         modal.hidden = !modal.hidden;
     }
 
-    public hasDialogs() {
-        return this.priorityModal || this.staticModal || this.modals.length > 0;
+    public hasDialogs(): boolean {
+        return !!this.priorityModal || !!this.staticModal || this.modals.length > 0;
     }
 
     public createDialog<T extends any[]>(
         Element: React.ComponentType<any>,
         ...rest: ParametersWithoutFirst<ModalManager["createDialogAsync"]>
-    ) {
+    ): IHandle<T> {
         return this.createDialogAsync<T>(Promise.resolve(Element), ...rest);
     }
 
     public appendDialog<T extends any[]>(
         Element: React.ComponentType,
         ...rest: ParametersWithoutFirst<ModalManager["appendDialogAsync"]>
-    ) {
+    ): IHandle<T> {
         return this.appendDialogAsync<T>(Promise.resolve(Element), ...rest);
     }
 
-    public closeCurrentModal(reason: string) {
+    public closeCurrentModal(reason: string): void {
         const modal = this.getCurrentModal();
         if (!modal) {
             return;
@@ -139,7 +139,11 @@ export class ModalManager extends TypedEventEmitter<ModalManagerEvent, HandlerMa
         props?: IProps<T>,
         className?: string,
         options?: IOptions<T>,
-    ) {
+    ): {
+        modal: IModal<T>;
+        closeDialog: IHandle<T>["close"];
+        onFinishedProm: IHandle<T>["finished"];
+    } {
         const modal: IModal<T> = {
             onFinished: props ? props.onFinished : null,
             onBeforeClose: options.onBeforeClose,
@@ -173,7 +177,7 @@ export class ModalManager extends TypedEventEmitter<ModalManagerEvent, HandlerMa
     ): [IHandle<T>["close"], IHandle<T>["finished"]] {
         const deferred = defer<T>();
         return [
-            async (...args: T) => {
+            async (...args: T): Promise<void> => {
                 if (modal.beforeClosePromise) {
                     await modal.beforeClosePromise;
                 } else if (modal.onBeforeClose) {
@@ -302,7 +306,7 @@ export class ModalManager extends TypedEventEmitter<ModalManagerEvent, HandlerMa
         }
     }
 
-    private onBackgroundClick = () => {
+    private onBackgroundClick = (): void => {
         const modal = this.getCurrentModal();
         if (!modal) {
             return;
@@ -320,7 +324,7 @@ export class ModalManager extends TypedEventEmitter<ModalManagerEvent, HandlerMa
         return this.priorityModal ? this.priorityModal : this.modals[0] || this.staticModal;
     }
 
-    private async reRender() {
+    private async reRender(): Promise<void> {
         // await next tick because sometimes ReactDOM can race with itself and cause the modal to wrongly stick around
         await sleep(0);
 

src/PlatformPeg.ts

@@ -32,13 +32,13 @@ import { PlatformSetPayload } from "./dispatcher/payloads/PlatformSetPayload";
  * object.
  */
 export class PlatformPeg {
-    private platform: BasePlatform = null;
+    private platform: BasePlatform | null = null;
 
     /**
      * Returns the current Platform object for the application.
      * This should be an instance of a class extending BasePlatform.
      */
-    public get() {
+    public get(): BasePlatform | null {
         return this.platform;
     }
 
@@ -46,7 +46,7 @@ export class PlatformPeg {
      * Sets the current platform handler object to use for the application.
      * @param {BasePlatform} platform an instance of a class extending BasePlatform.
      */
-    public set(platform: BasePlatform) {
+    public set(platform: BasePlatform): void {
         this.platform = platform;
         defaultDispatcher.dispatch<PlatformSetPayload>({
             action: Action.PlatformSet,

src/PosthogAnalytics.ts

@@ -175,7 +175,7 @@ export class PosthogAnalytics {
         this.onLayoutUpdated();
     }
 
-    private onLayoutUpdated = () => {
+    private onLayoutUpdated = (): void => {
         let layout: UserProperties["WebLayout"];
 
         switch (SettingsStore.getValue("layout")) {
@@ -195,7 +195,7 @@ export class PosthogAnalytics {
         this.setProperty("WebLayout", layout);
     };
 
-    private onAction = (payload: ActionPayload) => {
+    private onAction = (payload: ActionPayload): void => {
         if (payload.action !== Action.SettingUpdated) return;
         const settingsPayload = payload as SettingUpdatedPayload;
         if (["layout", "useCompactLayout"].includes(settingsPayload.settingName)) {
@@ -232,7 +232,7 @@ export class PosthogAnalytics {
         return properties;
     };
 
-    private registerSuperProperties(properties: Properties) {
+    private registerSuperProperties(properties: Properties): void {
         if (this.enabled) {
             this.posthog.register(properties);
         }
@@ -255,7 +255,7 @@ export class PosthogAnalytics {
     }
 
     // eslint-disable-nextline no-unused-varsx
-    private capture(eventName: string, properties: Properties, options?: IPostHogEventOptions) {
+    private capture(eventName: string, properties: Properties, options?: IPostHogEventOptions): void {
         if (!this.enabled) {
             return;
         }

src/PosthogTrackers.ts

@@ -107,20 +107,20 @@ export default class PosthogTrackers {
 }
 
 export class PosthogScreenTracker extends PureComponent<{ screenName: ScreenName }> {
-    public componentDidMount() {
+    public componentDidMount(): void {
         PosthogTrackers.instance.trackOverride(this.props.screenName);
     }
 
-    public componentDidUpdate() {
+    public componentDidUpdate(): void {
         // We do not clear the old override here so that we do not send the non-override screen as a transition
         PosthogTrackers.instance.trackOverride(this.props.screenName);
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         PosthogTrackers.instance.clearOverride(this.props.screenName);
     }
 
-    public render() {
+    public render(): JSX.Element {
         return null; // no need to render anything, we just need to hook into the React lifecycle
     }
 }

src/Presence.ts

@@ -41,7 +41,7 @@ class Presence {
      * Start listening the user activity to evaluate his presence state.
      * Any state change will be sent to the homeserver.
      */
-    public async start() {
+    public async start(): Promise<void> {
         this.unavailableTimer = new Timer(UNAVAILABLE_TIME_MS);
         // the user_activity_start action starts the timer
         this.dispatcherRef = dis.register(this.onAction);
@@ -58,7 +58,7 @@ class Presence {
     /**
      * Stop tracking user activity
      */
-    public stop() {
+    public stop(): void {
         if (this.dispatcherRef) {
             dis.unregister(this.dispatcherRef);
             this.dispatcherRef = null;
@@ -73,11 +73,11 @@ class Presence {
      * Get the current presence state.
      * @returns {string} the presence state (see PRESENCE enum)
      */
-    public getState() {
+    public getState(): State {
         return this.state;
     }
 
-    private onAction = (payload: ActionPayload) => {
+    private onAction = (payload: ActionPayload): void => {
         if (payload.action === "user_activity") {
             this.setState(State.Online);
             this.unavailableTimer.restart();
@@ -89,7 +89,7 @@ class Presence {
      * If the state has changed, the homeserver will be notified.
      * @param {string} newState the new presence state (see PRESENCE enum)
      */
-    private async setState(newState: State) {
+    private async setState(newState: State): Promise<void> {
         if (newState === this.state) {
             return;
         }

src/ScalarAuthClient.ts

@@ -49,7 +49,7 @@ export default class ScalarAuthClient {
         this.isDefaultManager = apiUrl === configApiUrl && configUiUrl === uiUrl;
     }
 
-    private writeTokenToStore() {
+    private writeTokenToStore(): void {
         window.localStorage.setItem("mx_scalar_token_at_" + this.apiUrl, this.scalarToken);
         if (this.isDefaultManager) {
             // We remove the old token from storage to migrate upwards. This is safe
@@ -72,7 +72,7 @@ export default class ScalarAuthClient {
         return this.readTokenFromStore();
     }
 
-    public setTermsInteractionCallback(callback) {
+    public setTermsInteractionCallback(callback: TermsInteractionCallback): void {
         this.termsInteractionCallback = callback;
     }
 

src/ScalarMessaging.ts

@@ -711,7 +711,7 @@ function returnStateEvent(event: MessageEvent<any>, roomId: string, eventType: s
     sendResponse(event, stateEvent.getContent());
 }
 
-async function getOpenIdToken(event: MessageEvent<any>) {
+async function getOpenIdToken(event: MessageEvent<any>): Promise<void> {
     try {
         const tokenObject = await MatrixClientPeg.get().getOpenIdToken();
         sendResponse(event, tokenObject);
@@ -728,7 +728,7 @@ async function sendEvent(
         content?: IContent;
     }>,
     roomId: string,
-) {
+): Promise<void> {
     const eventType = event.data.type;
     const stateKey = event.data.state_key;
     const content = event.data.content;
@@ -786,7 +786,7 @@ async function readEvents(
         limit?: number;
     }>,
     roomId: string,
-) {
+): Promise<void> {
     const eventType = event.data.type;
     const stateKey = event.data.state_key;
     const limit = event.data.limit;

src/SdkConfig.ts

@@ -56,7 +56,7 @@ export default class SdkConfig {
     private static instance: IConfigOptions;
     private static fallback: SnakedObject<IConfigOptions>;
 
-    private static setInstance(i: IConfigOptions) {
+    private static setInstance(i: IConfigOptions): void {
         SdkConfig.instance = i;
         SdkConfig.fallback = new SnakedObject(i);
 
@@ -90,18 +90,18 @@ export default class SdkConfig {
         return val === undefined ? undefined : null;
     }
 
-    public static put(cfg: Partial<IConfigOptions>) {
+    public static put(cfg: Partial<IConfigOptions>): void {
         SdkConfig.setInstance({ ...DEFAULTS, ...cfg });
     }
 
     /**
      * Resets the config to be completely empty.
      */
-    public static unset() {
+    public static unset(): void {
         SdkConfig.setInstance(<IConfigOptions>{}); // safe to cast - defaults will be applied
     }
 
-    public static add(cfg: Partial<IConfigOptions>) {
+    public static add(cfg: Partial<IConfigOptions>): void {
         SdkConfig.put({ ...SdkConfig.get(), ...cfg });
     }
 }

src/SecurityManager.ts

@@ -86,7 +86,7 @@ async function confirmToDismiss(): Promise<boolean> {
 type KeyParams = { passphrase: string; recoveryKey: string };
 
 function makeInputToKey(keyInfo: ISecretStorageKeyInfo): (keyParams: KeyParams) => Promise<Uint8Array> {
-    return async ({ passphrase, recoveryKey }) => {
+    return async ({ passphrase, recoveryKey }): Promise<Uint8Array> => {
         if (passphrase) {
             return deriveKey(passphrase, keyInfo.passphrase.salt, keyInfo.passphrase.iterations);
         } else {
@@ -151,7 +151,7 @@ async function getSecretStorageKey({
         /* props= */
         {
             keyInfo,
-            checkPrivateKey: async (input: KeyParams) => {
+            checkPrivateKey: async (input: KeyParams): Promise<boolean> => {
                 const key = await inputToKey(input);
                 return MatrixClientPeg.get().checkSecretStorageKey(key, keyInfo);
             },
@@ -160,7 +160,7 @@ async function getSecretStorageKey({
         /* isPriorityModal= */ false,
         /* isStaticModal= */ false,
         /* options= */ {
-            onBeforeClose: async (reason) => {
+            onBeforeClose: async (reason): Promise<boolean> => {
                 if (reason === "backgroundClick") {
                     return confirmToDismiss();
                 }
@@ -196,7 +196,7 @@ export async function getDehydrationKey(
         /* props= */
         {
             keyInfo,
-            checkPrivateKey: async (input) => {
+            checkPrivateKey: async (input): Promise<boolean> => {
                 const key = await inputToKey(input);
                 try {
                     checkFunc(key);
@@ -210,7 +210,7 @@ export async function getDehydrationKey(
         /* isPriorityModal= */ false,
         /* isStaticModal= */ false,
         /* options= */ {
-            onBeforeClose: async (reason) => {
+            onBeforeClose: async (reason): Promise<boolean> => {
                 if (reason === "backgroundClick") {
                     return confirmToDismiss();
                 }
@@ -324,7 +324,7 @@ export async function promptForBackupPassphrase(): Promise<Uint8Array> {
  * bootstrapped. Optional.
  * @param {bool} [forceReset] Reset secret storage even if it's already set up
  */
-export async function accessSecretStorage(func = async () => {}, forceReset = false) {
+export async function accessSecretStorage(func = async (): Promise<void> => {}, forceReset = false): Promise<void> {
     const cli = MatrixClientPeg.get();
     secretStorageBeingAccessed = true;
     try {
@@ -342,7 +342,7 @@ export async function accessSecretStorage(func = async () => {}, forceReset = fa
                 /* priority = */ false,
                 /* static = */ true,
                 /* options = */ {
-                    onBeforeClose: async (reason) => {
+                    onBeforeClose: async (reason): Promise<boolean> => {
                         // If Secure Backup is required, you cannot leave the modal.
                         if (reason === "backgroundClick") {
                             return !isSecureBackupRequired();
@@ -357,7 +357,7 @@ export async function accessSecretStorage(func = async () => {}, forceReset = fa
             }
         } else {
             await cli.bootstrapCrossSigning({
-                authUploadDeviceSigningKeys: async (makeRequest) => {
+                authUploadDeviceSigningKeys: async (makeRequest): Promise<void> => {
                     const { finished } = Modal.createDialog(InteractiveAuthDialog, {
                         title: _t("Setting up keys"),
                         matrixClient: cli,

src/SendHistoryManager.ts

@@ -60,7 +60,7 @@ export default class SendHistoryManager {
         };
     }
 
-    public save(editorModel: EditorModel, replyEvent?: MatrixEvent) {
+    public save(editorModel: EditorModel, replyEvent?: MatrixEvent): void {
         const item = SendHistoryManager.createItem(editorModel, replyEvent);
         this.history.push(item);
         this.currentIndex = this.history.length;

src/SlashCommands.tsx

@@ -85,7 +85,7 @@ const singleMxcUpload = async (): Promise<string | null> => {
 
             Modal.createDialog(UploadConfirmDialog, {
                 file,
-                onFinished: async (shouldContinue) => {
+                onFinished: async (shouldContinue): Promise<void> => {
                     if (shouldContinue) {
                         const { content_uri: uri } = await MatrixClientPeg.get().uploadContent(file);
                         resolve(uri);
@@ -151,11 +151,11 @@ export class Command {
         this.analyticsName = opts.analyticsName;
     }
 
-    public getCommand() {
+    public getCommand(): string {
         return `/${this.command}`;
     }
 
-    public getCommandWithArgs() {
+    public getCommandWithArgs(): string {
         return this.getCommand() + " " + this.args;
     }
 
@@ -184,7 +184,7 @@ export class Command {
         return this.runFn(roomId, args);
     }
 
-    public getUsage() {
+    public getUsage(): string {
         return _t("Usage") + ": " + this.getCommandWithArgs();
     }
 
@@ -193,15 +193,15 @@ export class Command {
     }
 }
 
-function reject(error) {
+function reject(error?: any): RunResult {
     return { error };
 }
 
-function success(promise?: Promise<any>) {
+function success(promise?: Promise<any>): RunResult {
     return { promise };
 }
 
-function successSync(value: any) {
+function successSync(value: any): RunResult {
     return success(Promise.resolve(value));
 }
 
@@ -319,7 +319,7 @@ export const Commands = [
                 );
 
                 return success(
-                    finished.then(async ([resp]) => {
+                    finished.then(async ([resp]): Promise<void> => {
                         if (!resp?.continue) return;
                         await upgradeRoom(room, args, resp.invite);
                     }),
@@ -338,7 +338,7 @@ export const Commands = [
         runFn: function (roomId, args) {
             if (args) {
                 return success(
-                    (async () => {
+                    (async (): Promise<void> => {
                         const unixTimestamp = Date.parse(args);
                         if (!unixTimestamp) {
                             throw newTranslatableError(
@@ -501,7 +501,9 @@ export const Commands = [
                 ? ContentHelpers.parseTopicContent(content)
                 : { text: _t("This room has no topic.") };
 
-            const ref = (e) => e && linkifyElement(e);
+            const ref = (e): void => {
+                if (e) linkifyElement(e);
+            };
             const body = topicToHtml(topic.text, topic.html, ref, true);
 
             Modal.createDialog(InfoDialog, {
@@ -1028,7 +1030,7 @@ export const Commands = [
                     const fingerprint = matches[3];
 
                     return success(
-                        (async () => {
+                        (async (): Promise<void> => {
                             const device = cli.getStoredDevice(userId, deviceId);
                             if (!device) {
                                 throw newTranslatableError("Unknown (user, session) pair: (%(userId)s, %(deviceId)s)", {
@@ -1205,7 +1207,7 @@ export const Commands = [
         },
         runFn: (roomId) => {
             return success(
-                (async () => {
+                (async (): Promise<void> => {
                     const room = await VoipUserMapper.sharedInstance().getVirtualRoomForRoom(roomId);
                     if (!room) throw newTranslatableError("No virtual room for this room");
                     dis.dispatch<ViewRoomPayload>({
@@ -1231,7 +1233,7 @@ export const Commands = [
             }
 
             return success(
-                (async () => {
+                (async (): Promise<void> => {
                     if (isPhoneNumber) {
                         const results = await LegacyCallHandler.instance.pstnLookup(userId);
                         if (!results || results.length === 0 || !results[0].userid) {
@@ -1265,7 +1267,7 @@ export const Commands = [
                     const [userId, msg] = matches.slice(1);
                     if (userId && userId.startsWith("@") && userId.includes(":")) {
                         return success(
-                            (async () => {
+                            (async (): Promise<void> => {
                                 const cli = MatrixClientPeg.get();
                                 const roomId = await ensureDMExists(cli, userId);
                                 dis.dispatch<ViewRoomPayload>({

src/SlidingSyncManager.ts

@@ -302,7 +302,7 @@ export class SlidingSyncManager {
      * @param batchSize The number of rooms to return in each request.
      * @param gapBetweenRequestsMs The number of milliseconds to wait between requests.
      */
-    public async startSpidering(batchSize: number, gapBetweenRequestsMs: number) {
+    public async startSpidering(batchSize: number, gapBetweenRequestsMs: number): Promise<void> {
         await sleep(gapBetweenRequestsMs); // wait a bit as this is called on first render so let's let things load
         const listIndex = this.getOrAllocateListIndex(SlidingSyncManager.ListSearch);
         let startIndex = batchSize;

src/Terms.ts

@@ -75,7 +75,7 @@ export type TermsInteractionCallback = (
 export async function startTermsFlow(
     services: Service[],
     interactionCallback: TermsInteractionCallback = dialogTermsInteractionCallback,
-) {
+): Promise<void> {
     const termsPromises = services.map((s) => MatrixClientPeg.get().getTerms(s.serviceType, s.baseUrl));
 
     /*
@@ -176,7 +176,7 @@ export async function startTermsFlow(
             urlsForService,
         );
     });
-    return Promise.all(agreePromises);
+    await Promise.all(agreePromises);
 }
 
 export async function dialogTermsInteractionCallback(

src/TextForEvent.tsx

@@ -228,7 +228,7 @@ function textForTombstoneEvent(ev: MatrixEvent): () => string | null {
     return () => _t("%(senderDisplayName)s upgraded this room.", { senderDisplayName });
 }
 
-const onViewJoinRuleSettingsClick = () => {
+const onViewJoinRuleSettingsClick = (): void => {
     defaultDispatcher.dispatch({
         action: "open_room_settings",
         initial_tab_id: ROOM_SECURITY_TAB,

src/UserActivity.ts

@@ -50,7 +50,7 @@ export default class UserActivity {
         this.activeRecentlyTimeout = new Timer(RECENTLY_ACTIVE_THRESHOLD_MS);
     }
 
-    public static sharedInstance() {
+    public static sharedInstance(): UserActivity {
         if (window.mxUserActivity === undefined) {
             window.mxUserActivity = new UserActivity(window, document);
         }
@@ -66,7 +66,7 @@ export default class UserActivity {
      * later on when the user does become active.
      * @param {Timer} timer the timer to use
      */
-    public timeWhileActiveNow(timer: Timer) {
+    public timeWhileActiveNow(timer: Timer): void {
         this.timeWhile(timer, this.attachedActiveNowTimers);
         if (this.userActiveNow()) {
             timer.start();
@@ -82,14 +82,14 @@ export default class UserActivity {
      * later on when the user does become active.
      * @param {Timer} timer the timer to use
      */
-    public timeWhileActiveRecently(timer: Timer) {
+    public timeWhileActiveRecently(timer: Timer): void {
         this.timeWhile(timer, this.attachedActiveRecentlyTimers);
         if (this.userActiveRecently()) {
             timer.start();
         }
     }
 
-    private timeWhile(timer: Timer, attachedTimers: Timer[]) {
+    private timeWhile(timer: Timer, attachedTimers: Timer[]): void {
         // important this happens first
         const index = attachedTimers.indexOf(timer);
         if (index === -1) {
@@ -113,7 +113,7 @@ export default class UserActivity {
     /**
      * Start listening to user activity
      */
-    public start() {
+    public start(): void {
         this.document.addEventListener("mousedown", this.onUserActivity);
         this.document.addEventListener("mousemove", this.onUserActivity);
         this.document.addEventListener("keydown", this.onUserActivity);
@@ -133,7 +133,7 @@ export default class UserActivity {
     /**
      * Stop tracking user activity
      */
-    public stop() {
+    public stop(): void {
         this.document.removeEventListener("mousedown", this.onUserActivity);
         this.document.removeEventListener("mousemove", this.onUserActivity);
         this.document.removeEventListener("keydown", this.onUserActivity);
@@ -152,7 +152,7 @@ export default class UserActivity {
      * user's attention at any given moment.
      * @returns {boolean} true if user is currently 'active'
      */
-    public userActiveNow() {
+    public userActiveNow(): boolean {
         return this.activeNowTimeout.isRunning();
     }
 
@@ -164,11 +164,11 @@ export default class UserActivity {
      * (or they may have gone to make tea and left the window focused).
      * @returns {boolean} true if user has been active recently
      */
-    public userActiveRecently() {
+    public userActiveRecently(): boolean {
         return this.activeRecentlyTimeout.isRunning();
     }
 
-    private onPageVisibilityChanged = (e) => {
+    private onPageVisibilityChanged = (e): void => {
         if (this.document.visibilityState === "hidden") {
             this.activeNowTimeout.abort();
             this.activeRecentlyTimeout.abort();
@@ -177,12 +177,12 @@ export default class UserActivity {
         }
     };
 
-    private onWindowBlurred = () => {
+    private onWindowBlurred = (): void => {
         this.activeNowTimeout.abort();
         this.activeRecentlyTimeout.abort();
     };
 
-    private onUserActivity = (event: MouseEvent) => {
+    private onUserActivity = (event: MouseEvent): void => {
         // ignore anything if the window isn't focused
         if (!this.document.hasFocus()) return;
 
@@ -214,7 +214,7 @@ export default class UserActivity {
         }
     };
 
-    private static async runTimersUntilTimeout(attachedTimers: Timer[], timeout: Timer) {
+    private static async runTimersUntilTimeout(attachedTimers: Timer[], timeout: Timer): Promise<void> {
         attachedTimers.forEach((t) => t.start());
         try {
             await timeout.finished();

src/accessibility/RovingTabIndex.tsx

@@ -87,7 +87,7 @@ interface IAction {
     };
 }
 
-export const reducer = (state: IState, action: IAction) => {
+export const reducer: Reducer<IState, IAction> = (state: IState, action: IAction) => {
     switch (action.type) {
         case Type.Register: {
             if (!state.activeRef) {

src/accessibility/Toolbar.tsx

@@ -26,7 +26,7 @@ interface IProps extends Omit<React.HTMLProps<HTMLDivElement>, "onKeyDown"> {}
 // https://www.w3.org/TR/wai-aria-practices-1.1/#toolbar
 // All buttons passed in children must use RovingTabIndex to set `onFocus`, `isActive`, `ref`
 const Toolbar: React.FC<IProps> = ({ children, ...props }) => {
-    const onKeyDown = (ev: React.KeyboardEvent) => {
+    const onKeyDown = (ev: React.KeyboardEvent): void => {
         const target = ev.target as HTMLElement;
         // Don't interfere with input default keydown behaviour
         if (target.tagName === "INPUT") return;

src/accessibility/context_menu/StyledMenuItemCheckbox.tsx

@@ -33,7 +33,7 @@ interface IProps extends React.ComponentProps<typeof StyledCheckbox> {
 export const StyledMenuItemCheckbox: React.FC<IProps> = ({ children, label, onChange, onClose, ...props }) => {
     const [onFocus, isActive, ref] = useRovingTabIndex<HTMLInputElement>();
 
-    const onKeyDown = (e: React.KeyboardEvent) => {
+    const onKeyDown = (e: React.KeyboardEvent): void => {
         let handled = true;
         const action = getKeyBindingsManager().getAccessibilityAction(e);
 
@@ -55,7 +55,7 @@ export const StyledMenuItemCheckbox: React.FC<IProps> = ({ children, label, onCh
             e.preventDefault();
         }
     };
-    const onKeyUp = (e: React.KeyboardEvent) => {
+    const onKeyUp = (e: React.KeyboardEvent): void => {
         const action = getKeyBindingsManager().getAccessibilityAction(e);
         switch (action) {
             case KeyBindingAction.Space:

src/accessibility/context_menu/StyledMenuItemRadio.tsx

@@ -33,7 +33,7 @@ interface IProps extends React.ComponentProps<typeof StyledRadioButton> {
 export const StyledMenuItemRadio: React.FC<IProps> = ({ children, label, onChange, onClose, ...props }) => {
     const [onFocus, isActive, ref] = useRovingTabIndex<HTMLInputElement>();
 
-    const onKeyDown = (e: React.KeyboardEvent) => {
+    const onKeyDown = (e: React.KeyboardEvent): void => {
         let handled = true;
         const action = getKeyBindingsManager().getAccessibilityAction(e);
 
@@ -55,7 +55,7 @@ export const StyledMenuItemRadio: React.FC<IProps> = ({ children, label, onChang
             e.preventDefault();
         }
     };
-    const onKeyUp = (e: React.KeyboardEvent) => {
+    const onKeyUp = (e: React.KeyboardEvent): void => {
         const action = getKeyBindingsManager().getAccessibilityAction(e);
         switch (action) {
             case KeyBindingAction.Enter:

src/actions/actionCreators.ts

@@ -15,7 +15,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { AsyncActionPayload } from "../dispatcher/payloads";
+import { AsyncActionFn, AsyncActionPayload } from "../dispatcher/payloads";
 
 /**
  * Create an action thunk that will dispatch actions indicating the current
@@ -45,7 +45,7 @@ import { AsyncActionPayload } from "../dispatcher/payloads";
  *                     `fn`.
  */
 export function asyncAction(id: string, fn: () => Promise<any>, pendingFn: () => any | null): AsyncActionPayload {
-    const helper = (dispatch) => {
+    const helper: AsyncActionFn = (dispatch) => {
         dispatch({
             action: id + ".pending",
             request: typeof pendingFn === "function" ? pendingFn() : undefined,

src/actions/handlers/viewUserDeviceSettings.ts

@@ -22,7 +22,7 @@ import defaultDispatcher from "../../dispatcher/dispatcher";
  * Redirect to the correct device manager section
  * Based on the labs setting
  */
-export const viewUserDeviceSettings = (isNewDeviceManagerEnabled: boolean) => {
+export const viewUserDeviceSettings = (isNewDeviceManagerEnabled: boolean): void => {
     defaultDispatcher.dispatch({
         action: Action.ViewUserSettings,
         initialTabId: isNewDeviceManagerEnabled ? UserTab.SessionManager : UserTab.Security,

src/async-components/views/dialogs/eventindex/ManageEventIndexDialog.tsx

@@ -56,7 +56,7 @@ export default class ManageEventIndexDialog extends React.Component<IProps, ISta
         };
     }
 
-    public updateCurrentRoom = async (room) => {
+    public updateCurrentRoom = async (room): Promise<void> => {
         const eventIndex = EventIndexPeg.get();
         let stats;
 
@@ -131,17 +131,17 @@ export default class ManageEventIndexDialog extends React.Component<IProps, ISta
         });
     }
 
-    private onDisable = async () => {
+    private onDisable = async (): Promise<void> => {
         const DisableEventIndexDialog = (await import("./DisableEventIndexDialog")).default;
         Modal.createDialog(DisableEventIndexDialog, null, null, /* priority = */ false, /* static = */ true);
     };
 
-    private onCrawlerSleepTimeChange = (e) => {
+    private onCrawlerSleepTimeChange = (e): void => {
         this.setState({ crawlerSleepTime: e.target.value });
         SettingsStore.setValue("crawlerSleepTime", null, SettingLevel.DEVICE, e.target.value);
     };
 
-    public render() {
+    public render(): JSX.Element {
         const brand = SdkConfig.get().brand;
 
         let crawlerState;

src/async-components/views/dialogs/security/CreateKeyBackupDialog.tsx

@@ -125,7 +125,7 @@ export default class CreateKeyBackupDialog extends React.PureComponent<IProps, I
         let info;
         try {
             if (secureSecretStorage) {
-                await accessSecretStorage(async () => {
+                await accessSecretStorage(async (): Promise<void> => {
                     info = await MatrixClientPeg.get().prepareKeyBackupVersion(null /* random key */, {
                         secureSecretStorage: true,
                     });

src/async-components/views/dialogs/security/CreateSecretStorageDialog.tsx

@@ -350,7 +350,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
                     createSecretStorageKey: async () => this.recoveryKey,
                     keyBackupInfo: this.state.backupInfo,
                     setupNewKeyBackup: !this.state.backupInfo,
-                    getKeyBackupPassphrase: async () => {
+                    getKeyBackupPassphrase: async (): Promise<Uint8Array> => {
                         // We may already have the backup key if we earlier went
                         // through the restore backup path, so pass it along
                         // rather than prompting again.
@@ -383,7 +383,9 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
     private restoreBackup = async (): Promise<void> => {
         // It's possible we'll need the backup key later on for bootstrapping,
         // so let's stash it here, rather than prompting for it twice.
-        const keyCallback = (k) => (this.backupKey = k);
+        const keyCallback = (k: Uint8Array): void => {
+            this.backupKey = k;
+        };
 
         const { finished } = Modal.createDialog(
             RestoreKeyBackupDialog,
@@ -420,7 +422,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
         this.setState({ phase: Phase.ChooseKeyPassphrase });
     };
 
-    private onPassPhraseNextClick = async (e: React.FormEvent) => {
+    private onPassPhraseNextClick = async (e: React.FormEvent): Promise<void> => {
         e.preventDefault();
         if (!this.passphraseField.current) return; // unmounting
 
@@ -434,7 +436,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
         this.setState({ phase: Phase.PassphraseConfirm });
     };
 
-    private onPassPhraseConfirmNextClick = async (e: React.FormEvent) => {
+    private onPassPhraseConfirmNextClick = async (e: React.FormEvent): Promise<void> => {
         e.preventDefault();
 
         if (this.state.passPhrase !== this.state.passPhraseConfirm) return;

src/async-components/views/dialogs/security/ExportE2eKeysDialog.tsx

@@ -121,7 +121,7 @@ export default class ExportE2eKeysDialog extends React.Component<IProps, IState>
         return false;
     };
 
-    private onPassphraseChange = (ev: React.ChangeEvent<HTMLInputElement>, phrase: AnyPassphrase) => {
+    private onPassphraseChange = (ev: React.ChangeEvent<HTMLInputElement>, phrase: AnyPassphrase): void => {
         this.setState({
             [phrase]: ev.target.value,
         } as Pick<IState, AnyPassphrase>);

src/async-components/views/dialogs/security/ImportE2eKeysDialog.tsx

@@ -91,7 +91,7 @@ export default class ImportE2eKeysDialog extends React.Component<IProps, IState>
         return false;
     };
 
-    private startImport(file: File, passphrase: string) {
+    private startImport(file: File, passphrase: string): Promise<void> {
         this.setState({
             errStr: null,
             phase: Phase.Importing,

src/audio/ManagedPlayback.ts

@@ -30,7 +30,7 @@ export class ManagedPlayback extends Playback {
         return super.play();
     }
 
-    public destroy() {
+    public destroy(): void {
         this.manager.destroyPlaybackInstance(this);
         super.destroy();
     }

src/audio/Playback.ts

@@ -145,7 +145,7 @@ export class Playback extends EventEmitter implements IDestroyable, PlaybackInte
         return true; // we don't ever care if the event had listeners, so just return "yes"
     }
 
-    public destroy() {
+    public destroy(): void {
         // Dev note: It's critical that we call stop() during cleanup to ensure that downstream callers
         // are aware of the final clock position before the user triggered an unload.
         // noinspection JSIgnoredPromiseFromCall - not concerned about being called async here
@@ -159,7 +159,7 @@ export class Playback extends EventEmitter implements IDestroyable, PlaybackInte
         }
     }
 
-    public async prepare() {
+    public async prepare(): Promise<void> {
         // don't attempt to decode the media again
         // AudioContext.decodeAudioData detaches the array buffer `this.buf`
         // meaning it cannot be re-read
@@ -190,7 +190,7 @@ export class Playback extends EventEmitter implements IDestroyable, PlaybackInte
                 this.context.decodeAudioData(
                     this.buf,
                     (b) => resolve(b),
-                    async (e) => {
+                    async (e): Promise<void> => {
                         try {
                             // This error handler is largely for Safari as well, which doesn't support Opus/Ogg
                             // very well.
@@ -232,12 +232,12 @@ export class Playback extends EventEmitter implements IDestroyable, PlaybackInte
         this.emit(PlaybackState.Stopped); // signal that we're not decoding anymore
     }
 
-    private onPlaybackEnd = async () => {
+    private onPlaybackEnd = async (): Promise<void> => {
         await this.context.suspend();
         this.emit(PlaybackState.Stopped);
     };
 
-    public async play() {
+    public async play(): Promise<void> {
         // We can't restart a buffer source, so we need to create a new one if we hit the end
         if (this.state === PlaybackState.Stopped) {
             this.disconnectSource();
@@ -256,13 +256,13 @@ export class Playback extends EventEmitter implements IDestroyable, PlaybackInte
         this.emit(PlaybackState.Playing);
     }
 
-    private disconnectSource() {
+    private disconnectSource(): void {
         if (this.element) return; // leave connected, we can (and must) re-use it
         this.source?.disconnect();
         this.source?.removeEventListener("ended", this.onPlaybackEnd);
     }
 
-    private makeNewSourceBuffer() {
+    private makeNewSourceBuffer(): void {
         if (this.element && this.source) return; // leave connected, we can (and must) re-use it
 
         if (this.element) {
@@ -276,22 +276,22 @@ export class Playback extends EventEmitter implements IDestroyable, PlaybackInte
         this.source.connect(this.context.destination);
     }
 
-    public async pause() {
+    public async pause(): Promise<void> {
         await this.context.suspend();
         this.emit(PlaybackState.Paused);
     }
 
-    public async stop() {
+    public async stop(): Promise<void> {
         await this.onPlaybackEnd();
         this.clock.flagStop();
     }
 
-    public async toggle() {
+    public async toggle(): Promise<void> {
         if (this.isPlaying) await this.pause();
         else await this.play();
     }
 
-    public async skipTo(timeSeconds: number) {
+    public async skipTo(timeSeconds: number): Promise<void> {
         // Dev note: this function talks a lot about clock desyncs. There is a clock running
         // independently to the audio context and buffer so that accurate human-perceptible
         // time can be exposed. The PlaybackClock class has more information, but the short

src/audio/PlaybackClock.ts

@@ -89,7 +89,7 @@ export class PlaybackClock implements IDestroyable {
         return this.observable;
     }
 
-    private checkTime = (force = false) => {
+    private checkTime = (force = false): void => {
         const now = this.timeSeconds; // calculated dynamically
         if (this.lastCheck !== now || force) {
             this.observable.update([now, this.durationSeconds]);
@@ -102,7 +102,7 @@ export class PlaybackClock implements IDestroyable {
      * The placeholders will be overridden once known.
      * @param {MatrixEvent} event The event to use for placeholders.
      */
-    public populatePlaceholdersFrom(event: MatrixEvent) {
+    public populatePlaceholdersFrom(event: MatrixEvent): void {
         const durationMs = Number(event.getContent()["info"]?.["duration"]);
         if (Number.isFinite(durationMs)) this.placeholderDuration = durationMs / 1000;
     }
@@ -112,11 +112,11 @@ export class PlaybackClock implements IDestroyable {
      * This is to ensure the clock isn't skewed into thinking it is ~0.5s into
      * a clip when the duration is set.
      */
-    public flagLoadTime() {
+    public flagLoadTime(): void {
         this.clipStart = this.context.currentTime;
     }
 
-    public flagStart() {
+    public flagStart(): void {
         if (this.stopped) {
             this.clipStart = this.context.currentTime;
             this.stopped = false;
@@ -128,7 +128,7 @@ export class PlaybackClock implements IDestroyable {
         }
     }
 
-    public flagStop() {
+    public flagStop(): void {
         this.stopped = true;
 
         // Reset the clock time now so that the update going out will trigger components
@@ -136,13 +136,13 @@ export class PlaybackClock implements IDestroyable {
         this.clipStart = this.context.currentTime;
     }
 
-    public syncTo(contextTime: number, clipTime: number) {
+    public syncTo(contextTime: number, clipTime: number): void {
         this.clipStart = contextTime - clipTime;
         this.stopped = false; // count as a mid-stream pause (if we were stopped)
         this.checkTime(true);
     }
 
-    public destroy() {
+    public destroy(): void {
         this.observable.close();
         if (this.timerId) clearInterval(this.timerId);
     }

src/audio/PlaybackManager.ts

@@ -38,13 +38,13 @@ export class PlaybackManager {
      * instances are paused.
      * @param playback Optional. The playback to leave untouched.
      */
-    public pauseAllExcept(playback?: Playback) {
+    public pauseAllExcept(playback?: Playback): void {
         this.instances
             .filter((p) => p !== playback && p.currentState === PlaybackState.Playing)
             .forEach((p) => p.pause());
     }
 
-    public destroyPlaybackInstance(playback: ManagedPlayback) {
+    public destroyPlaybackInstance(playback: ManagedPlayback): void {
         this.instances = this.instances.filter((p) => p !== playback);
     }
 

src/audio/PlaybackQueue.ts

@@ -75,28 +75,28 @@ export class PlaybackQueue {
         return queue;
     }
 
-    private persistClocks() {
+    private persistClocks(): void {
         localStorage.setItem(
             `mx_voice_message_clocks_${this.room.roomId}`,
             JSON.stringify(Array.from(this.clockStates.entries())),
         );
     }
 
-    private loadClocks() {
+    private loadClocks(): void {
         const val = localStorage.getItem(`mx_voice_message_clocks_${this.room.roomId}`);
         if (!!val) {
             this.clockStates = new Map<string, number>(JSON.parse(val));
         }
     }
 
-    public unsortedEnqueue(mxEvent: MatrixEvent, playback: Playback) {
+    public unsortedEnqueue(mxEvent: MatrixEvent, playback: Playback): void {
         // We don't ever detach our listeners: we expect the Playback to clean up for us
         this.playbacks.set(mxEvent.getId(), playback);
         playback.on(UPDATE_EVENT, (state) => this.onPlaybackStateChange(playback, mxEvent, state));
         playback.clockInfo.liveData.onUpdate((clock) => this.onPlaybackClock(playback, mxEvent, clock));
     }
 
-    private onPlaybackStateChange(playback: Playback, mxEvent: MatrixEvent, newState: PlaybackState) {
+    private onPlaybackStateChange(playback: Playback, mxEvent: MatrixEvent, newState: PlaybackState): void {
         // Remember where the user got to in playback
         const wasLastPlaying = this.currentPlaybackId === mxEvent.getId();
         if (newState === PlaybackState.Stopped && this.clockStates.has(mxEvent.getId()) && !wasLastPlaying) {
@@ -210,7 +210,7 @@ export class PlaybackQueue {
         }
     }
 
-    private onPlaybackClock(playback: Playback, mxEvent: MatrixEvent, clocks: number[]) {
+    private onPlaybackClock(playback: Playback, mxEvent: MatrixEvent, clocks: number[]): void {
         if (playback.currentState === PlaybackState.Decoding) return; // ignore pre-ready values
 
         if (playback.currentState !== PlaybackState.Stopped) {

src/audio/RecorderWorklet.ts

@@ -43,7 +43,7 @@ class MxVoiceWorklet extends AudioWorkletProcessor {
     private nextAmplitudeSecond = 0;
     private amplitudeIndex = 0;
 
-    public process(inputs, outputs, parameters) {
+    public process(inputs, outputs, parameters): boolean {
         const currentSecond = roundTimeToTargetFreq(currentTime);
         // We special case the first ping because there's a fairly good chance that we'll miss the zeroth
         // update. Firefox for instance takes 0.06 seconds (roughly) to call this function for the first

src/audio/VoiceMessageRecording.ts

@@ -141,7 +141,7 @@ export class VoiceMessageRecording implements IDestroyable {
         this.voiceRecording.destroy();
     }
 
-    private onDataAvailable = (data: ArrayBuffer) => {
+    private onDataAvailable = (data: ArrayBuffer): void => {
         const buf = new Uint8Array(data);
         this.buffer = concat(this.buffer, buf);
     };
@@ -153,6 +153,6 @@ export class VoiceMessageRecording implements IDestroyable {
     }
 }
 
-export const createVoiceMessageRecording = (matrixClient: MatrixClient) => {
+export const createVoiceMessageRecording = (matrixClient: MatrixClient): VoiceMessageRecording => {
     return new VoiceMessageRecording(matrixClient, new VoiceRecording());
 };

src/audio/VoiceRecording.ts

@@ -110,7 +110,7 @@ export class VoiceRecording extends EventEmitter implements IDestroyable {
         return !MediaDeviceHandler.getAudioNoiseSuppression();
     }
 
-    private async makeRecorder() {
+    private async makeRecorder(): Promise<void> {
         try {
             this.recorderStream = await navigator.mediaDevices.getUserMedia({
                 audio: {
@@ -212,14 +212,14 @@ export class VoiceRecording extends EventEmitter implements IDestroyable {
         return !!Recorder.isRecordingSupported();
     }
 
-    private onAudioProcess = (ev: AudioProcessingEvent) => {
+    private onAudioProcess = (ev: AudioProcessingEvent): void => {
         this.processAudioUpdate(ev.playbackTime);
 
         // We skip the functionality of the worklet regarding waveform calculations: we
         // should get that information pretty quick during the playback info.
     };
 
-    private processAudioUpdate = (timeSeconds: number) => {
+    private processAudioUpdate = (timeSeconds: number): void => {
         if (!this.recording) return;
 
         this.observable.update({
@@ -260,7 +260,7 @@ export class VoiceRecording extends EventEmitter implements IDestroyable {
     /**
      * {@link https://github.com/chris-rudmin/opus-recorder#instance-fields ref for recorderSeconds}
      */
-    public get recorderSeconds() {
+    public get recorderSeconds(): number {
         return this.recorder.encodedSamplePosition / 48000;
     }
 
@@ -279,7 +279,7 @@ export class VoiceRecording extends EventEmitter implements IDestroyable {
     }
 
     public async stop(): Promise<void> {
-        return Singleflight.for(this, "stop").do(async () => {
+        return Singleflight.for(this, "stop").do(async (): Promise<void> => {
             if (!this.recording) {
                 throw new Error("No recording to stop");
             }
@@ -307,7 +307,7 @@ export class VoiceRecording extends EventEmitter implements IDestroyable {
         });
     }
 
-    public destroy() {
+    public destroy(): void {
         // noinspection JSIgnoredPromiseFromCall - not concerned about stop() being called async here
         this.stop();
         this.removeAllListeners();

src/autocomplete/AutocompleteProvider.tsx

@@ -22,7 +22,7 @@ import { TimelineRenderingType } from "../contexts/RoomContext";
 import type { ICompletion, ISelectionRange } from "./Autocompleter";
 
 export interface ICommand {
-    command: string | null;
+    command: RegExpExecArray | null;
     range: {
         start: number;
         end: number;
@@ -59,7 +59,7 @@ export default abstract class AutocompleteProvider {
         }
     }
 
-    public destroy() {
+    public destroy(): void {
         // stub
     }
 
@@ -70,7 +70,7 @@ export default abstract class AutocompleteProvider {
      * @param {boolean} force True if the user is forcing completion
      * @return {object} { command, range } where both objects fields are null if no match
      */
-    public getCurrentCommand(query: string, selection: ISelectionRange, force = false) {
+    public getCurrentCommand(query: string, selection: ISelectionRange, force = false): ICommand {
         let commandRegex = this.commandRegex;
 
         if (force && this.shouldForceComplete()) {
@@ -83,7 +83,7 @@ export default abstract class AutocompleteProvider {
 
         commandRegex.lastIndex = 0;
 
-        let match;
+        let match: RegExpExecArray;
         while ((match = commandRegex.exec(query)) !== null) {
             const start = match.index;
             const end = start + match[0].length;

src/autocomplete/Autocompleter.ts

@@ -69,7 +69,7 @@ export default class Autocompleter {
         });
     }
 
-    public destroy() {
+    public destroy(): void {
         this.providers.forEach((p) => {
             p.destroy();
         });
@@ -88,7 +88,7 @@ export default class Autocompleter {
         */
         // list of results from each provider, each being a list of completions or null if it times out
         const completionsList: ICompletion[][] = await Promise.all(
-            this.providers.map(async (provider) => {
+            this.providers.map(async (provider): Promise<ICompletion[] | null> => {
                 return timeout(
                     provider.getCompletions(query, selection, force, limit),
                     null,

src/autocomplete/CommandProvider.tsx

@@ -100,7 +100,7 @@ export default class CommandProvider extends AutocompleteProvider {
             });
     }
 
-    public getName() {
+    public getName(): string {
         return "*️⃣ " + _t("Commands");
     }
 

src/autocomplete/EmojiProvider.tsx

@@ -55,7 +55,7 @@ const SORTED_EMOJI: ISortedEmoji[] = EMOJI.sort((a, b) => {
     _orderBy: index,
 }));
 
-function score(query, space) {
+function score(query: string, space: string): number {
     const index = space.indexOf(query);
     if (index === -1) {
         return Infinity;
@@ -154,7 +154,7 @@ export default class EmojiProvider extends AutocompleteProvider {
         return [];
     }
 
-    public getName() {
+    public getName(): string {
         return "😃 " + _t("Emoji");
     }
 

src/autocomplete/NotifProvider.tsx

@@ -65,7 +65,7 @@ export default class NotifProvider extends AutocompleteProvider {
         return [];
     }
 
-    public getName() {
+    public getName(): string {
         return "❗️ " + _t("Room Notification");
     }
 

src/autocomplete/QueryMatcher.ts

@@ -61,7 +61,7 @@ export default class QueryMatcher<T extends {}> {
         }
     }
 
-    public setObjects(objects: T[]) {
+    public setObjects(objects: T[]): void {
         this._items = new Map();
 
         for (const object of objects) {

src/autocomplete/RoomProvider.tsx

@@ -37,7 +37,15 @@ function canonicalScore(displayedAlias: string, room: Room): number {
     return displayedAlias === room.getCanonicalAlias() ? 0 : 1;
 }
 
-function matcherObject(room: Room, displayedAlias: string, matchName = "") {
+function matcherObject(
+    room: Room,
+    displayedAlias: string,
+    matchName = "",
+): {
+    room: Room;
+    matchName: string;
+    displayedAlias: string;
+} {
     return {
         room,
         matchName,
@@ -46,7 +54,7 @@ function matcherObject(room: Room, displayedAlias: string, matchName = "") {
 }
 
 export default class RoomProvider extends AutocompleteProvider {
-    protected matcher: QueryMatcher<Room>;
+    protected matcher: QueryMatcher<ReturnType<typeof matcherObject>>;
 
     public constructor(room: Room, renderingType?: TimelineRenderingType) {
         super({ commandRegex: ROOM_REGEX, renderingType });
@@ -55,7 +63,7 @@ export default class RoomProvider extends AutocompleteProvider {
         });
     }
 
-    protected getRooms() {
+    protected getRooms(): Room[] {
         const cli = MatrixClientPeg.get();
 
         // filter out spaces here as they get their own autocomplete provider
@@ -68,7 +76,6 @@ export default class RoomProvider extends AutocompleteProvider {
         force = false,
         limit = -1,
     ): Promise<ICompletion[]> {
-        let completions = [];
         const { command, range } = this.getCurrentCommand(query, selection, force);
         if (command) {
             // the only reason we need to do this is because Fuse only matches on properties
@@ -96,15 +103,15 @@ export default class RoomProvider extends AutocompleteProvider {
 
             this.matcher.setObjects(matcherObjects);
             const matchedString = command[0];
-            completions = this.matcher.match(matchedString, limit);
+            let completions = this.matcher.match(matchedString, limit);
             completions = sortBy(completions, [
                 (c) => canonicalScore(c.displayedAlias, c.room),
                 (c) => c.displayedAlias.length,
             ]);
             completions = uniqBy(completions, (match) => match.room);
-            completions = completions
-                .map((room) => {
-                    return {
+            return completions
+                .map(
+                    (room): ICompletion => ({
                         completion: room.displayedAlias,
                         completionId: room.room.roomId,
                         type: "room",
@@ -116,14 +123,14 @@ export default class RoomProvider extends AutocompleteProvider {
                             </PillCompletion>
                         ),
                         range,
-                    };
-                })
+                    }),
+                )
                 .filter((completion) => !!completion.completion && completion.completion.length > 0);
         }
-        return completions;
+        return [];
     }
 
-    public getName() {
+    public getName(): string {
         return _t("Rooms");
     }
 

src/autocomplete/SpaceProvider.tsx

@@ -14,6 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+import { Room } from "matrix-js-sdk/src/models/room";
 import React from "react";
 
 import { _t } from "../languageHandler";
@@ -21,13 +22,13 @@ import { MatrixClientPeg } from "../MatrixClientPeg";
 import RoomProvider from "./RoomProvider";
 
 export default class SpaceProvider extends RoomProvider {
-    protected getRooms() {
+    protected getRooms(): Room[] {
         return MatrixClientPeg.get()
             .getVisibleRooms()
             .filter((r) => r.isSpaceRoom());
     }
 
-    public getName() {
+    public getName(): string {
         return _t("Spaces");
     }
 

src/autocomplete/UserProvider.tsx

@@ -64,7 +64,7 @@ export default class UserProvider extends AutocompleteProvider {
         MatrixClientPeg.get().on(RoomStateEvent.Update, this.onRoomStateUpdate);
     }
 
-    public destroy() {
+    public destroy(): void {
         if (MatrixClientPeg.get()) {
             MatrixClientPeg.get().removeListener(RoomEvent.Timeline, this.onRoomTimeline);
             MatrixClientPeg.get().removeListener(RoomStateEvent.Update, this.onRoomStateUpdate);
@@ -77,7 +77,7 @@ export default class UserProvider extends AutocompleteProvider {
         toStartOfTimeline: boolean,
         removed: boolean,
         data: IRoomTimelineData,
-    ) => {
+    ): void => {
         if (!room) return; // notification timeline, we'll get this event again with a room specific timeline
         if (removed) return;
         if (room.roomId !== this.room.roomId) return;
@@ -93,7 +93,7 @@ export default class UserProvider extends AutocompleteProvider {
         this.onUserSpoke(ev.sender);
     };
 
-    private onRoomStateUpdate = (state: RoomState) => {
+    private onRoomStateUpdate = (state: RoomState): void => {
         // ignore updates in other rooms
         if (state.roomId !== this.room.roomId) return;
 
@@ -150,7 +150,7 @@ export default class UserProvider extends AutocompleteProvider {
         return _t("Users");
     }
 
-    private makeUsers() {
+    private makeUsers(): void {
         const events = this.room.getLiveTimeline().getEvents();
         const lastSpoken = {};
 
@@ -167,7 +167,7 @@ export default class UserProvider extends AutocompleteProvider {
         this.matcher.setObjects(this.users);
     }
 
-    public onUserSpoke(user: RoomMember) {
+    public onUserSpoke(user: RoomMember): void {
         if (!this.users) return;
         if (!user) return;
         if (user.userId === MatrixClientPeg.get().credentials.userId) return;

src/components/structures/AutoHideScrollbar.tsx

@@ -22,7 +22,7 @@ type DynamicHtmlElementProps<T extends keyof JSX.IntrinsicElements> =
     JSX.IntrinsicElements[T] extends HTMLAttributes<{}> ? DynamicElementProps<T> : DynamicElementProps<"div">;
 type DynamicElementProps<T extends keyof JSX.IntrinsicElements> = Partial<Omit<JSX.IntrinsicElements[T], "ref">>;
 
-export type IProps<T extends keyof JSX.IntrinsicElements> = DynamicHtmlElementProps<T> & {
+export type IProps<T extends keyof JSX.IntrinsicElements> = Omit<DynamicHtmlElementProps<T>, "onScroll"> & {
     element?: T;
     className?: string;
     onScroll?: (event: Event) => void;
@@ -39,7 +39,7 @@ export default class AutoHideScrollbar<T extends keyof JSX.IntrinsicElements> ex
 
     public readonly containerRef: React.RefObject<HTMLDivElement> = React.createRef();
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         if (this.containerRef.current && this.props.onScroll) {
             // Using the passive option to not block the main thread
             // https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener#improving_scrolling_performance_with_passive_listeners
@@ -49,13 +49,13 @@ export default class AutoHideScrollbar<T extends keyof JSX.IntrinsicElements> ex
         this.props.wrappedRef?.(this.containerRef.current);
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         if (this.containerRef.current && this.props.onScroll) {
             this.containerRef.current.removeEventListener("scroll", this.props.onScroll);
         }
     }
 
-    public render() {
+    public render(): JSX.Element {
         // eslint-disable-next-line @typescript-eslint/no-unused-vars
         const { element, className, onScroll, tabIndex, wrappedRef, children, ...otherProps } = this.props;
 

src/components/structures/AutocompleteInput.tsx

@@ -52,11 +52,11 @@ export const AutocompleteInput: React.FC<AutocompleteInputProps> = ({
     const editorContainerRef = useRef<HTMLDivElement>(null);
     const editorRef = useRef<HTMLInputElement>(null);
 
-    const focusEditor = () => {
+    const focusEditor = (): void => {
         editorRef?.current?.focus();
     };
 
-    const onQueryChange = async (e: ChangeEvent<HTMLInputElement>) => {
+    const onQueryChange = async (e: ChangeEvent<HTMLInputElement>): Promise<void> => {
         const value = e.target.value.trim();
         setQuery(value);
 
@@ -74,11 +74,11 @@ export const AutocompleteInput: React.FC<AutocompleteInputProps> = ({
         setSuggestions(matches);
     };
 
-    const onClickInputArea = () => {
+    const onClickInputArea = (): void => {
         focusEditor();
     };
 
-    const onKeyDown = (e: KeyboardEvent) => {
+    const onKeyDown = (e: KeyboardEvent): void => {
         const hasModifiers = e.ctrlKey || e.shiftKey || e.metaKey;
 
         // when the field is empty and the user hits backspace remove the right-most target
@@ -87,7 +87,7 @@ export const AutocompleteInput: React.FC<AutocompleteInputProps> = ({
         }
     };
 
-    const toggleSelection = (completion: ICompletion) => {
+    const toggleSelection = (completion: ICompletion): void => {
         const newSelection = [...selection];
         const index = selection.findIndex((selection) => selection.completionId === completion.completionId);
 
@@ -101,7 +101,7 @@ export const AutocompleteInput: React.FC<AutocompleteInputProps> = ({
         focusEditor();
     };
 
-    const removeSelection = (completion: ICompletion) => {
+    const removeSelection = (completion: ICompletion): void => {
         const newSelection = [...selection];
         const index = selection.findIndex((selection) => selection.completionId === completion.completionId);
 

src/components/structures/ContextMenu.tsx

@@ -64,7 +64,7 @@ export enum ChevronFace {
     None = "none",
 }
 
-export interface IProps extends IPosition {
+export interface MenuProps extends IPosition {
     menuWidth?: number;
     menuHeight?: number;
 
@@ -77,7 +77,9 @@ export interface IProps extends IPosition {
     menuPaddingRight?: number;
 
     zIndex?: number;
+}
 
+export interface IProps extends MenuProps {
     // If true, insert an invisible screen-sized element behind the menu that when clicked will close it.
     hasBackground?: boolean;
     // whether this context menu should be focus managed. If false it must handle itself
@@ -128,21 +130,21 @@ export default class ContextMenu extends React.PureComponent<IProps, IState> {
         this.initialFocus = document.activeElement as HTMLElement;
     }
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         Modal.on(ModalManagerEvent.Opened, this.onModalOpen);
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         Modal.off(ModalManagerEvent.Opened, this.onModalOpen);
         // return focus to the thing which had it before us
         this.initialFocus.focus();
     }
 
-    private onModalOpen = () => {
+    private onModalOpen = (): void => {
         this.props.onFinished?.();
     };
 
-    private collectContextMenuRect = (element: HTMLDivElement) => {
+    private collectContextMenuRect = (element: HTMLDivElement): void => {
         // We don't need to clean up when unmounting, so ignore
         if (!element) return;
 
@@ -159,7 +161,7 @@ export default class ContextMenu extends React.PureComponent<IProps, IState> {
         });
     };
 
-    private onContextMenu = (e) => {
+    private onContextMenu = (e: React.MouseEvent): void => {
         if (this.props.onFinished) {
             this.props.onFinished();
 
@@ -184,20 +186,20 @@ export default class ContextMenu extends React.PureComponent<IProps, IState> {
         }
     };
 
-    private onContextMenuPreventBubbling = (e) => {
+    private onContextMenuPreventBubbling = (e: React.MouseEvent): void => {
         // stop propagation so that any context menu handlers don't leak out of this context menu
         // but do not inhibit the default browser menu
         e.stopPropagation();
     };
 
     // Prevent clicks on the background from going through to the component which opened the menu.
-    private onFinished = (ev: React.MouseEvent) => {
+    private onFinished = (ev: React.MouseEvent): void => {
         ev.stopPropagation();
         ev.preventDefault();
         this.props.onFinished?.();
     };
 
-    private onClick = (ev: React.MouseEvent) => {
+    private onClick = (ev: React.MouseEvent): void => {
         // Don't allow clicks to escape the context menu wrapper
         ev.stopPropagation();
 
@@ -208,7 +210,7 @@ export default class ContextMenu extends React.PureComponent<IProps, IState> {
 
     // We now only handle closing the ContextMenu in this keyDown handler.
     // All of the item/option navigation is delegated to RovingTabIndex.
-    private onKeyDown = (ev: React.KeyboardEvent) => {
+    private onKeyDown = (ev: React.KeyboardEvent): void => {
         ev.stopPropagation(); // prevent keyboard propagating out of the context menu, we're focus-locked
 
         const action = getKeyBindingsManager().getAccessibilityAction(ev);
@@ -243,7 +245,7 @@ export default class ContextMenu extends React.PureComponent<IProps, IState> {
         }
     };
 
-    protected renderMenu(hasBackground = this.props.hasBackground) {
+    protected renderMenu(hasBackground = this.props.hasBackground): JSX.Element {
         const position: Partial<Writeable<DOMRect>> = {};
         const {
             top,
@@ -501,17 +503,13 @@ export const toLeftOrRightOf = (elementRect: DOMRect, chevronOffset = 12): ToRig
     return toRightOf(elementRect, chevronOffset);
 };
 
-export type AboveLeftOf = IPosition & {
-    chevronFace: ChevronFace;
-};
-
 // Placement method for <ContextMenu /> to position context menu right-aligned and flowing to the left of elementRect,
 // and either above or below: wherever there is more space (maybe this should be aboveOrBelowLeftOf?)
 export const aboveLeftOf = (
     elementRect: Pick<DOMRect, "right" | "top" | "bottom">,
     chevronFace = ChevronFace.None,
     vPadding = 0,
-): AboveLeftOf => {
+): MenuProps => {
     const menuOptions: IPosition & { chevronFace: ChevronFace } = { chevronFace };
 
     const buttonRight = elementRect.right + window.scrollX;
@@ -535,7 +533,7 @@ export const aboveRightOf = (
     elementRect: Pick<DOMRect, "left" | "top" | "bottom">,
     chevronFace = ChevronFace.None,
     vPadding = 0,
-): AboveLeftOf => {
+): MenuProps => {
     const menuOptions: IPosition & { chevronFace: ChevronFace } = { chevronFace };
 
     const buttonLeft = elementRect.left + window.scrollX;
@@ -555,11 +553,11 @@ export const aboveRightOf = (
 
 // Placement method for <ContextMenu /> to position context menu right-aligned and flowing to the left of elementRect
 // and always above elementRect
-export const alwaysAboveLeftOf = (
+export const alwaysMenuProps = (
     elementRect: Pick<DOMRect, "right" | "bottom" | "top">,
     chevronFace = ChevronFace.None,
     vPadding = 0,
-) => {
+): IPosition & { chevronFace: ChevronFace } => {
     const menuOptions: IPosition & { chevronFace: ChevronFace } = { chevronFace };
 
     const buttonRight = elementRect.right + window.scrollX;
@@ -578,7 +576,7 @@ export const alwaysAboveRightOf = (
     elementRect: Pick<DOMRect, "left" | "top">,
     chevronFace = ChevronFace.None,
     vPadding = 0,
-) => {
+): IPosition & { chevronFace: ChevronFace } => {
     const menuOptions: IPosition & { chevronFace: ChevronFace } = { chevronFace };
 
     const buttonLeft = elementRect.left + window.scrollX;
@@ -607,12 +605,12 @@ export const useContextMenu = <T extends any = HTMLElement>(inputRef?: RefObject
     }
 
     const [isOpen, setIsOpen] = useState(false);
-    const open = (ev?: SyntheticEvent) => {
+    const open = (ev?: SyntheticEvent): void => {
         ev?.preventDefault();
         ev?.stopPropagation();
         setIsOpen(true);
     };
-    const close = (ev?: SyntheticEvent) => {
+    const close = (ev?: SyntheticEvent): void => {
         ev?.preventDefault();
         ev?.stopPropagation();
         setIsOpen(false);
@@ -622,8 +620,11 @@ export const useContextMenu = <T extends any = HTMLElement>(inputRef?: RefObject
 };
 
 // XXX: Deprecated, used only for dynamic Tooltips. Avoid using at all costs.
-export function createMenu(ElementClass, props) {
-    const onFinished = function (...args) {
+export function createMenu(
+    ElementClass: typeof React.Component,
+    props: Record<string, any>,
+): { close: (...args: any[]) => void } {
+    const onFinished = function (...args): void {
         ReactDOM.unmountComponentAtNode(getOrCreateContainer());
         props?.onFinished?.apply(null, args);
     };

src/components/structures/EmbeddedPage.tsx

@@ -60,7 +60,7 @@ export default class EmbeddedPage extends React.PureComponent<IProps, IState> {
         return sanitizeHtml(_t(s));
     }
 
-    private async fetchEmbed() {
+    private async fetchEmbed(): Promise<void> {
         let res: Response;
 
         try {

src/components/structures/FileDropTarget.tsx

@@ -37,7 +37,7 @@ const FileDropTarget: React.FC<IProps> = ({ parent, onFileDrop }) => {
     useEffect(() => {
         if (!parent || parent.ondrop) return;
 
-        const onDragEnter = (ev: DragEvent) => {
+        const onDragEnter = (ev: DragEvent): void => {
             ev.stopPropagation();
             ev.preventDefault();
 
@@ -55,7 +55,7 @@ const FileDropTarget: React.FC<IProps> = ({ parent, onFileDrop }) => {
             }));
         };
 
-        const onDragLeave = (ev: DragEvent) => {
+        const onDragLeave = (ev: DragEvent): void => {
             ev.stopPropagation();
             ev.preventDefault();
 
@@ -65,7 +65,7 @@ const FileDropTarget: React.FC<IProps> = ({ parent, onFileDrop }) => {
             }));
         };
 
-        const onDragOver = (ev: DragEvent) => {
+        const onDragOver = (ev: DragEvent): void => {
             ev.stopPropagation();
             ev.preventDefault();
 
@@ -79,7 +79,7 @@ const FileDropTarget: React.FC<IProps> = ({ parent, onFileDrop }) => {
             }
         };
 
-        const onDrop = (ev: DragEvent) => {
+        const onDrop = (ev: DragEvent): void => {
             ev.stopPropagation();
             ev.preventDefault();
             onFileDrop(ev.dataTransfer);

src/components/structures/FilePanel.tsx

@@ -223,7 +223,7 @@ class FilePanel extends React.Component<IProps, IState> {
         }
     }
 
-    public render() {
+    public render(): JSX.Element {
         if (MatrixClientPeg.get().isGuest()) {
             return (
                 <BaseCard className="mx_FilePanel mx_RoomView_messageListWrapper" onClose={this.props.onClose}>

src/components/structures/GenericErrorPage.tsx

@@ -22,7 +22,7 @@ interface IProps {
 }
 
 export default class GenericErrorPage extends React.PureComponent<IProps> {
-    public render() {
+    public render(): JSX.Element {
         return (
             <div className="mx_GenericErrorPage">
                 <div className="mx_GenericErrorPage_box">

src/components/structures/HomePage.tsx

@@ -33,17 +33,17 @@ import MiniAvatarUploader, { AVATAR_SIZE } from "../views/elements/MiniAvatarUpl
 import PosthogTrackers from "../../PosthogTrackers";
 import EmbeddedPage from "./EmbeddedPage";
 
-const onClickSendDm = (ev: ButtonEvent) => {
+const onClickSendDm = (ev: ButtonEvent): void => {
     PosthogTrackers.trackInteraction("WebHomeCreateChatButton", ev);
     dis.dispatch({ action: "view_create_chat" });
 };
 
-const onClickExplore = (ev: ButtonEvent) => {
+const onClickExplore = (ev: ButtonEvent): void => {
     PosthogTrackers.trackInteraction("WebHomeExploreRoomsButton", ev);
     dis.fire(Action.ViewRoomDirectory);
 };
 
-const onClickNewRoom = (ev: ButtonEvent) => {
+const onClickNewRoom = (ev: ButtonEvent): void => {
     PosthogTrackers.trackInteraction("WebHomeCreateRoomButton", ev);
     dis.dispatch({ action: "view_create_room" });
 };
@@ -52,12 +52,17 @@ interface IProps {
     justRegistered?: boolean;
 }
 
-const getOwnProfile = (userId: string) => ({
+const getOwnProfile = (
+    userId: string,
+): {
+    displayName: string;
+    avatarUrl: string;
+} => ({
     displayName: OwnProfileStore.instance.displayName || userId,
     avatarUrl: OwnProfileStore.instance.getHttpAvatarUrl(AVATAR_SIZE),
 });
 
-const UserWelcomeTop = () => {
+const UserWelcomeTop: React.FC = () => {
     const cli = useContext(MatrixClientContext);
     const userId = cli.getUserId();
     const [ownProfile, setOwnProfile] = useState(getOwnProfile(userId));

src/components/structures/HostSignupAction.tsx

@@ -28,7 +28,7 @@ interface IProps {
 interface IState {}
 
 export default class HostSignupAction extends React.PureComponent<IProps, IState> {
-    private openDialog = async () => {
+    private openDialog = async (): Promise<void> => {
         this.props.onClick?.();
         await HostSignupStore.instance.setHostSignupActive(true);
     };

src/components/structures/InteractiveAuth.tsx

@@ -130,7 +130,7 @@ export default class InteractiveAuthComponent extends React.Component<IProps, IS
         }
     }
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         this.authLogic
             .attemptAuth()
             .then((result) => {
@@ -155,7 +155,7 @@ export default class InteractiveAuthComponent extends React.Component<IProps, IS
             });
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         this.unmounted = true;
 
         if (this.intervalId !== null) {
@@ -249,7 +249,7 @@ export default class InteractiveAuthComponent extends React.Component<IProps, IS
         this.authLogic.setEmailSid(sid);
     };
 
-    public render() {
+    public render(): JSX.Element {
         const stage = this.state.authStage;
         if (!stage) {
             if (this.state.busy) {

src/components/structures/LeftPanel.tsx

@@ -89,7 +89,7 @@ export default class LeftPanel extends React.Component<IProps, IState> {
         return SettingsStore.getValue("feature_breadcrumbs_v2") ? BreadcrumbsMode.Labs : BreadcrumbsMode.Legacy;
     }
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         UIStore.instance.trackElementDimensions("ListContainer", this.listContainerRef.current);
         UIStore.instance.on("ListContainer", this.refreshStickyHeaders);
         // Using the passive option to not block the main thread
@@ -97,7 +97,7 @@ export default class LeftPanel extends React.Component<IProps, IState> {
         this.listContainerRef.current?.addEventListener("scroll", this.onScroll, { passive: true });
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         BreadcrumbsStore.instance.off(UPDATE_EVENT, this.onBreadcrumbsUpdate);
         RoomListStore.instance.off(LISTS_UPDATE_EVENT, this.onBreadcrumbsUpdate);
         SpaceStore.instance.off(UPDATE_SELECTED_SPACE, this.updateActiveSpace);
@@ -112,25 +112,25 @@ export default class LeftPanel extends React.Component<IProps, IState> {
         }
     }
 
-    private updateActiveSpace = (activeSpace: SpaceKey) => {
+    private updateActiveSpace = (activeSpace: SpaceKey): void => {
         this.setState({ activeSpace });
     };
 
-    private onDialPad = () => {
+    private onDialPad = (): void => {
         dis.fire(Action.OpenDialPad);
     };
 
-    private onExplore = (ev: ButtonEvent) => {
+    private onExplore = (ev: ButtonEvent): void => {
         dis.fire(Action.ViewRoomDirectory);
         PosthogTrackers.trackInteraction("WebLeftPanelExploreRoomsButton", ev);
     };
 
-    private refreshStickyHeaders = () => {
+    private refreshStickyHeaders = (): void => {
         if (!this.listContainerRef.current) return; // ignore: no headers to sticky
         this.handleStickyHeaders(this.listContainerRef.current);
     };
 
-    private onBreadcrumbsUpdate = () => {
+    private onBreadcrumbsUpdate = (): void => {
         const newVal = LeftPanel.breadcrumbsMode;
         if (newVal !== this.state.showBreadcrumbs) {
             this.setState({ showBreadcrumbs: newVal });
@@ -141,7 +141,7 @@ export default class LeftPanel extends React.Component<IProps, IState> {
         }
     };
 
-    private handleStickyHeaders(list: HTMLDivElement) {
+    private handleStickyHeaders(list: HTMLDivElement): void {
         if (this.isDoingStickyHeaders) return;
         this.isDoingStickyHeaders = true;
         window.requestAnimationFrame(() => {
@@ -150,7 +150,7 @@ export default class LeftPanel extends React.Component<IProps, IState> {
         });
     }
 
-    private doStickyHeaders(list: HTMLDivElement) {
+    private doStickyHeaders(list: HTMLDivElement): void {
         const topEdge = list.scrollTop;
         const bottomEdge = list.offsetHeight + list.scrollTop;
         const sublists = list.querySelectorAll<HTMLDivElement>(".mx_RoomSublist:not(.mx_RoomSublist_hidden)");
@@ -282,20 +282,20 @@ export default class LeftPanel extends React.Component<IProps, IState> {
         }
     }
 
-    private onScroll = (ev: Event) => {
+    private onScroll = (ev: Event): void => {
         const list = ev.target as HTMLDivElement;
         this.handleStickyHeaders(list);
     };
 
-    private onFocus = (ev: React.FocusEvent) => {
+    private onFocus = (ev: React.FocusEvent): void => {
         this.focusedElement = ev.target;
     };
 
-    private onBlur = () => {
+    private onBlur = (): void => {
         this.focusedElement = null;
     };
 
-    private onKeyDown = (ev: React.KeyboardEvent, state?: IRovingTabIndexState) => {
+    private onKeyDown = (ev: React.KeyboardEvent, state?: IRovingTabIndexState): void => {
         if (!this.focusedElement) return;
 
         const action = getKeyBindingsManager().getRoomListAction(ev);

src/components/structures/LegacyCallEventGrouper.ts

@@ -142,7 +142,7 @@ export default class LegacyCallEventGrouper extends EventEmitter {
         return [...this.events][0]?.getRoomId();
     }
 
-    private onSilencedCallsChanged = () => {
+    private onSilencedCallsChanged = (): void => {
         const newState = LegacyCallHandler.instance.isCallSilenced(this.callId);
         this.emit(LegacyCallEventGrouperEvent.SilencedChanged, newState);
     };
@@ -163,20 +163,20 @@ export default class LegacyCallEventGrouper extends EventEmitter {
         LegacyCallHandler.instance.placeCall(this.roomId, this.isVoice ? CallType.Voice : CallType.Video);
     };
 
-    public toggleSilenced = () => {
+    public toggleSilenced = (): void => {
         const silenced = LegacyCallHandler.instance.isCallSilenced(this.callId);
         silenced
             ? LegacyCallHandler.instance.unSilenceCall(this.callId)
             : LegacyCallHandler.instance.silenceCall(this.callId);
     };
 
-    private setCallListeners() {
+    private setCallListeners(): void {
         if (!this.call) return;
         this.call.addListener(CallEvent.State, this.setState);
         this.call.addListener(CallEvent.LengthChanged, this.onLengthChanged);
     }
 
-    private setState = () => {
+    private setState = (): void => {
         if (CONNECTING_STATES.includes(this.call?.state)) {
             this.state = CallState.Connecting;
         } else if (SUPPORTED_STATES.includes(this.call?.state)) {
@@ -190,7 +190,7 @@ export default class LegacyCallEventGrouper extends EventEmitter {
         this.emit(LegacyCallEventGrouperEvent.StateChanged, this.state);
     };
 
-    private setCall = () => {
+    private setCall = (): void => {
         if (this.call) return;
 
         this.call = LegacyCallHandler.instance.getCallById(this.callId);
@@ -198,7 +198,7 @@ export default class LegacyCallEventGrouper extends EventEmitter {
         this.setState();
     };
 
-    public add(event: MatrixEvent) {
+    public add(event: MatrixEvent): void {
         if (this.events.has(event)) return; // nothing to do
         this.events.add(event);
         this.setCall();

src/components/structures/LoggedInView.tsx

@@ -159,7 +159,7 @@ class LoggedInView extends React.Component<IProps, IState> {
         this.resizeHandler = React.createRef();
     }
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         document.addEventListener("keydown", this.onNativeKeyDown, false);
         LegacyCallHandler.instance.addListener(LegacyCallHandlerEvent.CallState, this.onCallState);
 
@@ -191,7 +191,7 @@ class LoggedInView extends React.Component<IProps, IState> {
         this.refreshBackgroundImage();
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         document.removeEventListener("keydown", this.onNativeKeyDown, false);
         LegacyCallHandler.instance.removeListener(LegacyCallHandlerEvent.CallState, this.onCallState);
         this._matrixClient.removeListener(ClientEvent.AccountData, this.onAccountData);
@@ -221,14 +221,14 @@ class LoggedInView extends React.Component<IProps, IState> {
         this.setState({ backgroundImage });
     };
 
-    public canResetTimelineInRoom = (roomId: string) => {
+    public canResetTimelineInRoom = (roomId: string): boolean => {
         if (!this._roomView.current) {
             return true;
         }
         return this._roomView.current.canResetTimeline();
     };
 
-    private createResizer() {
+    private createResizer(): Resizer {
         let panelSize;
         let panelCollapsed;
         const collapseConfig: ICollapseConfig = {
@@ -268,7 +268,7 @@ class LoggedInView extends React.Component<IProps, IState> {
         return resizer;
     }
 
-    private loadResizerPreferences() {
+    private loadResizerPreferences(): void {
         let lhsSize = parseInt(window.localStorage.getItem("mx_lhs_size"), 10);
         if (isNaN(lhsSize)) {
             lhsSize = 350;
@@ -276,13 +276,13 @@ class LoggedInView extends React.Component<IProps, IState> {
         this.resizer.forHandleWithId("lp-resizer").resize(lhsSize);
     }
 
-    private onAccountData = (event: MatrixEvent) => {
+    private onAccountData = (event: MatrixEvent): void => {
         if (event.getType() === "m.ignored_user_list") {
             dis.dispatch({ action: "ignore_state_changed" });
         }
     };
 
-    private onCompactLayoutChanged = () => {
+    private onCompactLayoutChanged = (): void => {
         this.setState({
             useCompactLayout: SettingsStore.getValue("useCompactLayout"),
         });
@@ -311,13 +311,13 @@ class LoggedInView extends React.Component<IProps, IState> {
         }
     };
 
-    private onUsageLimitDismissed = () => {
+    private onUsageLimitDismissed = (): void => {
         this.setState({
             usageLimitDismissed: true,
         });
     };
 
-    private calculateServerLimitToast(syncError: IState["syncErrorData"], usageLimitEventContent?: IUsageLimit) {
+    private calculateServerLimitToast(syncError: IState["syncErrorData"], usageLimitEventContent?: IUsageLimit): void {
         const error = (syncError?.error as MatrixError)?.errcode === "M_RESOURCE_LIMIT_EXCEEDED";
         if (error) {
             usageLimitEventContent = (syncError?.error as MatrixError).data as IUsageLimit;
@@ -337,9 +337,9 @@ class LoggedInView extends React.Component<IProps, IState> {
         }
     }
 
-    private updateServerNoticeEvents = async () => {
+    private updateServerNoticeEvents = async (): Promise<void> => {
         const serverNoticeList = RoomListStore.instance.orderedLists[DefaultTagID.ServerNotice];
-        if (!serverNoticeList) return [];
+        if (!serverNoticeList) return;
 
         const events = [];
         let pinnedEventTs = 0;
@@ -379,7 +379,7 @@ class LoggedInView extends React.Component<IProps, IState> {
         });
     };
 
-    private onPaste = (ev: ClipboardEvent) => {
+    private onPaste = (ev: ClipboardEvent): void => {
         const element = ev.target as HTMLElement;
         const inputableElement = getInputableElement(element);
         if (inputableElement === document.activeElement) return; // nothing to do
@@ -422,13 +422,13 @@ class LoggedInView extends React.Component<IProps, IState> {
     We also listen with a native listener on the document to get keydown events when no element is focused.
     Bubbling is irrelevant here as the target is the body element.
     */
-    private onReactKeyDown = (ev) => {
+    private onReactKeyDown = (ev): void => {
         // events caught while bubbling up on the root element
         // of this component, so something must be focused.
         this.onKeyDown(ev);
     };
 
-    private onNativeKeyDown = (ev) => {
+    private onNativeKeyDown = (ev): void => {
         // only pass this if there is no focused element.
         // if there is, onKeyDown will be called by the
         // react keydown handler that respects the react bubbling order.
@@ -437,7 +437,7 @@ class LoggedInView extends React.Component<IProps, IState> {
         }
     };
 
-    private onKeyDown = (ev) => {
+    private onKeyDown = (ev): void => {
         let handled = false;
 
         const roomAction = getKeyBindingsManager().getRoomAction(ev);
@@ -615,13 +615,13 @@ class LoggedInView extends React.Component<IProps, IState> {
      * dispatch a page-up/page-down/etc to the appropriate component
      * @param {Object} ev The key event
      */
-    private onScrollKeyPressed = (ev) => {
+    private onScrollKeyPressed = (ev): void => {
         if (this._roomView.current) {
             this._roomView.current.handleScrollKey(ev);
         }
     };
 
-    public render() {
+    public render(): JSX.Element {
         let pageElement;
 
         switch (this.props.page_type) {

src/components/structures/MatrixChat.tsx

@@ -216,7 +216,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         realQueryParams: {},
         startingFragmentQueryParams: {},
         config: {},
-        onTokenLoginCompleted: () => {},
+        onTokenLoginCompleted: (): void => {},
     };
 
     private firstSyncComplete = false;
@@ -317,7 +317,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
                 this.props.realQueryParams,
                 this.props.defaultDeviceDisplayName,
                 this.getFragmentAfterLogin(),
-            ).then(async (loggedIn) => {
+            ).then(async (loggedIn): Promise<boolean | void> => {
                 if (this.props.realQueryParams?.loginToken) {
                     // remove the loginToken from the URL regardless
                     this.props.onTokenLoginCompleted();
@@ -353,7 +353,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         initSentry(SdkConfig.get("sentry"));
     }
 
-    private async postLoginSetup() {
+    private async postLoginSetup(): Promise<void> {
         const cli = MatrixClientPeg.get();
         const cryptoEnabled = cli.isCryptoEnabled();
         if (!cryptoEnabled) {
@@ -367,7 +367,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
             // as a proxy to figure out if it's worth prompting the user to verify
             // from another device.
             promisesList.push(
-                (async () => {
+                (async (): Promise<void> => {
                     crossSigningIsSetUp = await cli.userHasCrossSigningKeys();
                 })(),
             );
@@ -417,7 +417,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         window.addEventListener("resize", this.onWindowResized);
     }
 
-    public componentDidUpdate(prevProps, prevState) {
+    public componentDidUpdate(prevProps, prevState): void {
         if (this.shouldTrackPageChange(prevState, this.state)) {
             const durationMs = this.stopPageChangeTimer();
             PosthogTrackers.instance.trackPageChange(this.state.view, this.state.page_type, durationMs);
@@ -428,7 +428,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         }
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         Lifecycle.stopMatrixClient();
         dis.unregister(this.dispatcherRef);
         this.themeWatcher.stop();
@@ -477,7 +477,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         }
     }
 
-    private getServerProperties() {
+    private getServerProperties(): { serverConfig: ValidatedServerConfig } {
         let props = this.state.serverConfig;
         if (!props) props = this.props.serverConfig; // for unit tests
         if (!props) props = SdkConfig.get("validated_server_config");
@@ -513,11 +513,11 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         // to try logging out.
     }
 
-    private startPageChangeTimer() {
+    private startPageChangeTimer(): void {
         PerformanceMonitor.instance.start(PerformanceEntryNames.PAGE_CHANGE);
     }
 
-    private stopPageChangeTimer() {
+    private stopPageChangeTimer(): number | null {
         const perfMonitor = PerformanceMonitor.instance;
 
         perfMonitor.stop(PerformanceEntryNames.PAGE_CHANGE);
@@ -876,13 +876,13 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         }
     };
 
-    private setPage(pageType: PageType) {
+    private setPage(pageType: PageType): void {
         this.setState({
             page_type: pageType,
         });
     }
 
-    private async startRegistration(params: { [key: string]: string }) {
+    private async startRegistration(params: { [key: string]: string }): Promise<void> {
         const newState: Partial<IState> = {
             view: Views.REGISTER,
         };
@@ -916,7 +916,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
     }
 
     // switch view to the given room
-    private async viewRoom(roomInfo: ViewRoomPayload) {
+    private async viewRoom(roomInfo: ViewRoomPayload): Promise<void> {
         this.focusComposer = true;
 
         if (roomInfo.room_alias) {
@@ -992,7 +992,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         );
     }
 
-    private viewSomethingBehindModal() {
+    private viewSomethingBehindModal(): void {
         if (this.state.view !== Views.LOGGED_IN) {
             this.viewWelcome();
             return;
@@ -1002,7 +1002,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         }
     }
 
-    private viewWelcome() {
+    private viewWelcome(): void {
         if (shouldUseLoginForWelcome(SdkConfig.get())) {
             return this.viewLogin();
         }
@@ -1014,7 +1014,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         this.themeWatcher.recheck();
     }
 
-    private viewLogin(otherState?: any) {
+    private viewLogin(otherState?: any): void {
         this.setStateForNewView({
             view: Views.LOGIN,
             ...otherState,
@@ -1024,7 +1024,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         this.themeWatcher.recheck();
     }
 
-    private viewHome(justRegistered = false) {
+    private viewHome(justRegistered = false): void {
         // The home page requires the "logged in" view, so we'll set that.
         this.setStateForNewView({
             view: Views.LOGGED_IN,
@@ -1037,7 +1037,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         this.themeWatcher.recheck();
     }
 
-    private viewUser(userId: string, subAction: string) {
+    private viewUser(userId: string, subAction: string): void {
         // Wait for the first sync so that `getRoom` gives us a room object if it's
         // in the sync response
         const waitForSync = this.firstSyncPromise ? this.firstSyncPromise.promise : Promise.resolve();
@@ -1052,7 +1052,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         });
     }
 
-    private async createRoom(defaultPublic = false, defaultName?: string, type?: RoomType) {
+    private async createRoom(defaultPublic = false, defaultName?: string, type?: RoomType): Promise<void> {
         const modal = Modal.createDialog(CreateRoomDialog, {
             type,
             defaultPublic,
@@ -1065,7 +1065,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         }
     }
 
-    private chatCreateOrReuse(userId: string) {
+    private chatCreateOrReuse(userId: string): void {
         const snakedConfig = new SnakedObject<IConfigOptions>(this.props.config);
         // Use a deferred action to reshow the dialog once the user has registered
         if (MatrixClientPeg.get().isGuest()) {
@@ -1115,11 +1115,11 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         }
     }
 
-    private leaveRoomWarnings(roomId: string) {
+    private leaveRoomWarnings(roomId: string): JSX.Element[] {
         const roomToLeave = MatrixClientPeg.get().getRoom(roomId);
         const isSpace = roomToLeave?.isSpaceRoom();
         // Show a warning if there are additional complications.
-        const warnings = [];
+        const warnings: JSX.Element[] = [];
 
         const memberCount = roomToLeave.currentState.getJoinedMemberCount();
         if (memberCount === 1) {
@@ -1153,7 +1153,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         return warnings;
     }
 
-    private leaveRoom(roomId: string) {
+    private leaveRoom(roomId: string): void {
         const roomToLeave = MatrixClientPeg.get().getRoom(roomId);
         const warnings = this.leaveRoomWarnings(roomId);
 
@@ -1184,7 +1184,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         });
     }
 
-    private forgetRoom(roomId: string) {
+    private forgetRoom(roomId: string): void {
         const room = MatrixClientPeg.get().getRoom(roomId);
         MatrixClientPeg.get()
             .forget(roomId)
@@ -1208,7 +1208,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
             });
     }
 
-    private async copyRoom(roomId: string) {
+    private async copyRoom(roomId: string): Promise<void> {
         const roomLink = makeRoomPermalink(roomId);
         const success = await copyPlaintext(roomLink);
         if (!success) {
@@ -1223,13 +1223,13 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
      * Starts a chat with the welcome user, if the user doesn't already have one
      * @returns {string} The room ID of the new room, or null if no room was created
      */
-    private async startWelcomeUserChat() {
+    private async startWelcomeUserChat(): Promise<string | null> {
         // We can end up with multiple tabs post-registration where the user
         // might then end up with a session and we don't want them all making
         // a chat with the welcome user: try to de-dupe.
         // We need to wait for the first sync to complete for this to
         // work though.
-        let waitFor;
+        let waitFor: Promise<void>;
         if (!this.firstSyncComplete) {
             waitFor = this.firstSyncPromise.promise;
         } else {
@@ -1254,7 +1254,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
             // run without the update to m.direct, making another welcome
             // user room (it doesn't wait for new data from the server, just
             // the saved sync to be loaded).
-            const saveWelcomeUser = (ev: MatrixEvent) => {
+            const saveWelcomeUser = (ev: MatrixEvent): void => {
                 if (ev.getType() === EventType.Direct && ev.getContent()[snakedConfig.get("welcome_user_id")]) {
                     MatrixClientPeg.get().store.save(true);
                     MatrixClientPeg.get().removeListener(ClientEvent.AccountData, saveWelcomeUser);
@@ -1270,7 +1270,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
     /**
      * Called when a new logged in session has started
      */
-    private async onLoggedIn() {
+    private async onLoggedIn(): Promise<void> {
         ThemeController.isLogin = false;
         this.themeWatcher.recheck();
         StorageManager.tryPersistStorage();
@@ -1301,7 +1301,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         }
     }
 
-    private async onShowPostLoginScreen(useCase?: UseCase) {
+    private async onShowPostLoginScreen(useCase?: UseCase): Promise<void> {
         if (useCase) {
             PosthogAnalytics.instance.setProperty("ftueUseCaseSelection", useCase);
             SettingsStore.setValue("FTUE.useCaseSelection", null, SettingLevel.ACCOUNT, useCase);
@@ -1370,7 +1370,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         }
     }
 
-    private initPosthogAnalyticsToast() {
+    private initPosthogAnalyticsToast(): void {
         // Show the analytics toast if necessary
         if (SettingsStore.getValue("pseudonymousAnalyticsOptIn") === null) {
             showAnalyticsToast();
@@ -1397,7 +1397,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         );
     }
 
-    private showScreenAfterLogin() {
+    private showScreenAfterLogin(): void {
         // If screenAfterLogin is set, use that, then null it so that a second login will
         // result in view_home_page, _user_settings or _room_directory
         if (this.screenAfterLogin && this.screenAfterLogin.screen) {
@@ -1415,7 +1415,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         }
     }
 
-    private viewLastRoom() {
+    private viewLastRoom(): void {
         dis.dispatch<ViewRoomPayload>({
             action: Action.ViewRoom,
             room_id: localStorage.getItem("mx_last_room_id"),
@@ -1426,7 +1426,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
     /**
      * Called when the session is logged out
      */
-    private onLoggedOut() {
+    private onLoggedOut(): void {
         this.viewLogin({
             ready: false,
             collapseLhs: false,
@@ -1439,7 +1439,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
     /**
      * Called when the session is softly logged out
      */
-    private onSoftLogout() {
+    private onSoftLogout(): void {
         this.notifyNewScreen("soft_logout");
         this.setStateForNewView({
             view: Views.SOFT_LOGOUT,
@@ -1455,7 +1455,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
      * Called just before the matrix client is started
      * (useful for setting listeners)
      */
-    private onWillStartClient() {
+    private onWillStartClient(): void {
         // reset the 'have completed first sync' flag,
         // since we're about to start the client and therefore about
         // to do the first sync
@@ -1610,7 +1610,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
                     break;
             }
         });
-        cli.on(CryptoEvent.KeyBackupFailed, async (errcode) => {
+        cli.on(CryptoEvent.KeyBackupFailed, async (errcode): Promise<void> => {
             let haveNewVersion;
             let newVersionInfo;
             // if key backup is still enabled, there must be a new backup in place
@@ -1678,7 +1678,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
      * setting up anything that requires the client to be started.
      * @private
      */
-    private onClientStarted() {
+    private onClientStarted(): void {
         const cli = MatrixClientPeg.get();
 
         if (cli.isCryptoEnabled()) {
@@ -1700,7 +1700,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         }
     }
 
-    public showScreen(screen: string, params?: { [key: string]: any }) {
+    public showScreen(screen: string, params?: { [key: string]: any }): void {
         const cli = MatrixClientPeg.get();
         const isLoggedOutOrGuest = !cli || cli.isGuest();
         if (!isLoggedOutOrGuest && AUTH_SCREENS.includes(screen)) {
@@ -1861,14 +1861,14 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         }
     }
 
-    private notifyNewScreen(screen: string, replaceLast = false) {
+    private notifyNewScreen(screen: string, replaceLast = false): void {
         if (this.props.onNewScreen) {
             this.props.onNewScreen(screen, replaceLast);
         }
         this.setPageSubtitle();
     }
 
-    private onLogoutClick(event: React.MouseEvent<HTMLAnchorElement, MouseEvent>) {
+    private onLogoutClick(event: React.MouseEvent<HTMLAnchorElement, MouseEvent>): void {
         dis.dispatch({
             action: "logout",
         });
@@ -1876,7 +1876,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         event.preventDefault();
     }
 
-    private handleResize = () => {
+    private handleResize = (): void => {
         const LHS_THRESHOLD = 1000;
         const width = UIStore.instance.windowWidth;
 
@@ -1892,19 +1892,19 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         this.state.resizeNotifier.notifyWindowResized();
     };
 
-    private dispatchTimelineResize() {
+    private dispatchTimelineResize(): void {
         dis.dispatch({ action: "timeline_resize" });
     }
 
-    private onRegisterClick = () => {
+    private onRegisterClick = (): void => {
         this.showScreen("register");
     };
 
-    private onLoginClick = () => {
+    private onLoginClick = (): void => {
         this.showScreen("login");
     };
 
-    private onForgotPasswordClick = () => {
+    private onForgotPasswordClick = (): void => {
         this.showScreen("forgot_password");
     };
 
@@ -1926,7 +1926,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         });
     }
 
-    private setPageSubtitle(subtitle = "") {
+    private setPageSubtitle(subtitle = ""): void {
         if (this.state.currentRoomId) {
             const client = MatrixClientPeg.get();
             const room = client && client.getRoom(this.state.currentRoomId);
@@ -1963,11 +1963,11 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         this.setPageSubtitle();
     };
 
-    private onServerConfigChange = (serverConfig: ValidatedServerConfig) => {
+    private onServerConfigChange = (serverConfig: ValidatedServerConfig): void => {
         this.setState({ serverConfig });
     };
 
-    private makeRegistrationUrl = (params: QueryDict) => {
+    private makeRegistrationUrl = (params: QueryDict): string => {
         if (this.props.startingFragmentQueryParams.referrer) {
             params.referrer = this.props.startingFragmentQueryParams.referrer;
         }
@@ -2016,7 +2016,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         return fragmentAfterLogin;
     }
 
-    public render() {
+    public render(): JSX.Element {
         const fragmentAfterLogin = this.getFragmentAfterLogin();
         let view = null;
 
@@ -2132,7 +2132,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
                 />
             );
         } else if (this.state.view === Views.USE_CASE_SELECTION) {
-            view = <UseCaseSelection onFinished={(useCase) => this.onShowPostLoginScreen(useCase)} />;
+            view = <UseCaseSelection onFinished={(useCase): Promise<void> => this.onShowPostLoginScreen(useCase)} />;
         } else {
             logger.error(`Unknown view ${this.state.view}`);
         }

src/components/structures/MessagePanel.tsx

@@ -296,19 +296,19 @@ export default class MessagePanel extends React.Component<IProps, IState> {
         );
     }
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         this.calculateRoomMembersCount();
         this.props.room?.currentState.on(RoomStateEvent.Update, this.calculateRoomMembersCount);
         this.isMounted = true;
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         this.isMounted = false;
         this.props.room?.currentState.off(RoomStateEvent.Update, this.calculateRoomMembersCount);
         SettingsStore.unwatchSetting(this.showTypingNotificationsWatcherRef);
     }
 
-    public componentDidUpdate(prevProps, prevState) {
+    public componentDidUpdate(prevProps, prevState): void {
         if (prevProps.layout !== this.props.layout) {
             this.calculateRoomMembersCount();
         }
@@ -752,7 +752,7 @@ export default class MessagePanel extends React.Component<IProps, IState> {
         const readReceipts = this.readReceiptsByEvent[eventId];
 
         let isLastSuccessful = false;
-        const isSentState = (s) => !s || s === "sent";
+        const isSentState = (s): boolean => !s || s === "sent";
         const isSent = isSentState(mxEv.getAssociatedStatus());
         const hasNextEvent = nextEvent && this.shouldShowEvent(nextEvent);
         if (!hasNextEvent && isSent) {
@@ -982,7 +982,7 @@ export default class MessagePanel extends React.Component<IProps, IState> {
         }
     }
 
-    public render() {
+    public render(): JSX.Element {
         let topSpinner;
         let bottomSpinner;
         if (this.props.backPaginating) {

src/components/structures/NonUrgentToastContainer.tsx

@@ -37,15 +37,15 @@ export default class NonUrgentToastContainer extends React.PureComponent<IProps,
         NonUrgentToastStore.instance.on(UPDATE_EVENT, this.onUpdateToasts);
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         NonUrgentToastStore.instance.off(UPDATE_EVENT, this.onUpdateToasts);
     }
 
-    private onUpdateToasts = () => {
+    private onUpdateToasts = (): void => {
         this.setState({ toasts: NonUrgentToastStore.instance.components });
     };
 
-    public render() {
+    public render(): JSX.Element {
         const toasts = this.state.toasts.map((t, i) => {
             return (
                 <div className="mx_NonUrgentToastContainer_toast" key={`toast-${i}`}>

src/components/structures/NotificationPanel.tsx

@@ -55,7 +55,7 @@ export default class NotificationPanel extends React.PureComponent<IProps, IStat
         this.setState({ narrow });
     };
 
-    public render() {
+    public render(): JSX.Element {
         const emptyState = (
             <div className="mx_RightPanel_empty mx_NotificationPanel_empty">
                 <h2>{_t("You're all caught up")}</h2>

src/components/structures/PictureInPictureDragger.tsx

@@ -79,7 +79,7 @@ export default class PictureInPictureDragger extends React.Component<IProps> {
         this._moving = value;
     }
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         document.addEventListener("mousemove", this.onMoving);
         document.addEventListener("mouseup", this.onEndMoving);
         UIStore.instance.on(UI_EVENTS.Resize, this.onResize);
@@ -87,7 +87,7 @@ export default class PictureInPictureDragger extends React.Component<IProps> {
         this.snap();
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         document.removeEventListener("mousemove", this.onMoving);
         document.removeEventListener("mouseup", this.onEndMoving);
         UIStore.instance.off(UI_EVENTS.Resize, this.onResize);
@@ -97,7 +97,7 @@ export default class PictureInPictureDragger extends React.Component<IProps> {
         if (prevProps.children !== this.props.children) this.snap(true);
     }
 
-    private animationCallback = () => {
+    private animationCallback = (): void => {
         if (
             !this.moving &&
             Math.abs(this.translationX - this.desiredTranslationX) <= 1 &&
@@ -119,13 +119,13 @@ export default class PictureInPictureDragger extends React.Component<IProps> {
         this.props.onMove?.();
     };
 
-    private setStyle = () => {
+    private setStyle = (): void => {
         if (!this.callViewWrapper.current) return;
         // Set the element's style directly, bypassing React for efficiency
         this.callViewWrapper.current.style.transform = `translateX(${this.translationX}px) translateY(${this.translationY}px)`;
     };
 
-    private setTranslation(inTranslationX: number, inTranslationY: number) {
+    private setTranslation(inTranslationX: number, inTranslationY: number): void {
         const width = this.callViewWrapper.current?.clientWidth || PIP_VIEW_WIDTH;
         const height = this.callViewWrapper.current?.clientHeight || PIP_VIEW_HEIGHT;
 
@@ -152,7 +152,7 @@ export default class PictureInPictureDragger extends React.Component<IProps> {
         this.snap(false);
     };
 
-    private snap = (animate = false) => {
+    private snap = (animate = false): void => {
         const translationX = this.desiredTranslationX;
         const translationY = this.desiredTranslationY;
         // We subtract the PiP size from the window size in order to calculate
@@ -187,14 +187,14 @@ export default class PictureInPictureDragger extends React.Component<IProps> {
         this.scheduledUpdate.mark();
     };
 
-    private onStartMoving = (event: React.MouseEvent | MouseEvent) => {
+    private onStartMoving = (event: React.MouseEvent | MouseEvent): void => {
         event.preventDefault();
         event.stopPropagation();
 
         this.mouseHeld = true;
     };
 
-    private onMoving = (event: MouseEvent) => {
+    private onMoving = (event: MouseEvent): void => {
         if (!this.mouseHeld) return;
 
         event.preventDefault();
@@ -210,7 +210,7 @@ export default class PictureInPictureDragger extends React.Component<IProps> {
         this.setTranslation(event.pageX - this.initX, event.pageY - this.initY);
     };
 
-    private onEndMoving = (event: MouseEvent) => {
+    private onEndMoving = (event: MouseEvent): void => {
         if (!this.mouseHeld) return;
 
         event.preventDefault();
@@ -223,7 +223,7 @@ export default class PictureInPictureDragger extends React.Component<IProps> {
         this.snap(true);
     };
 
-    private onClickCapture = (event: React.MouseEvent) => {
+    private onClickCapture = (event: React.MouseEvent): void => {
         // To prevent mouse up events during dragging from being double-counted
         // as clicks, we cancel clicks before they ever reach the target
         if (this.moving) {
@@ -232,7 +232,7 @@ export default class PictureInPictureDragger extends React.Component<IProps> {
         }
     };
 
-    public render() {
+    public render(): JSX.Element {
         const style = {
             transform: `translateX(${this.translationX}px) translateY(${this.translationY}px)`,
         };

src/components/structures/PipContainer.tsx

@@ -135,7 +135,7 @@ class PipContainerInner extends React.Component<IProps, IState> {
         };
     }
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         LegacyCallHandler.instance.addListener(LegacyCallHandlerEvent.CallChangeRoom, this.updateCalls);
         LegacyCallHandler.instance.addListener(LegacyCallHandlerEvent.CallState, this.updateCalls);
         SdkContextClass.instance.roomViewStore.addListener(UPDATE_EVENT, this.onRoomViewStoreUpdate);
@@ -149,7 +149,7 @@ class PipContainerInner extends React.Component<IProps, IState> {
         ActiveWidgetStore.instance.on(ActiveWidgetStoreEvent.Undock, this.onWidgetDockChanges);
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         LegacyCallHandler.instance.removeListener(LegacyCallHandlerEvent.CallChangeRoom, this.updateCalls);
         LegacyCallHandler.instance.removeListener(LegacyCallHandlerEvent.CallState, this.updateCalls);
         const cli = MatrixClientPeg.get();
@@ -164,9 +164,9 @@ class PipContainerInner extends React.Component<IProps, IState> {
         ActiveWidgetStore.instance.off(ActiveWidgetStoreEvent.Undock, this.onWidgetDockChanges);
     }
 
-    private onMove = () => this.props.movePersistedElement.current?.();
+    private onMove = (): void => this.props.movePersistedElement.current?.();
 
-    private onRoomViewStoreUpdate = () => {
+    private onRoomViewStoreUpdate = (): void => {
         const newRoomId = SdkContextClass.instance.roomViewStore.getRoomId();
         const oldRoomId = this.state.viewedRoomId;
         if (newRoomId === oldRoomId) return;
@@ -213,7 +213,7 @@ class PipContainerInner extends React.Component<IProps, IState> {
         this.updateShowWidgetInPip();
     };
 
-    private onCallRemoteHold = () => {
+    private onCallRemoteHold = (): void => {
         if (!this.state.viewedRoomId) return;
         const [primaryCall, secondaryCalls] = getPrimarySecondaryCallsForPip(this.state.viewedRoomId);
 
@@ -238,7 +238,7 @@ class PipContainerInner extends React.Component<IProps, IState> {
     public updateShowWidgetInPip(
         persistentWidgetId = this.state.persistentWidgetId,
         persistentRoomId = this.state.persistentRoomId,
-    ) {
+    ): void {
         let fromAnotherRoom = false;
         let notDocked = false;
         // Sanity check the room - the widget may have been destroyed between render cycles, and
@@ -293,7 +293,7 @@ class PipContainerInner extends React.Component<IProps, IState> {
         );
     }
 
-    public render() {
+    public render(): JSX.Element {
         const pipMode = true;
         let pipContent: Array<CreatePipChildren> = [];
 

src/components/structures/RightPanel.tsx

@@ -101,7 +101,7 @@ export default class RightPanel extends React.Component<IProps, IState> {
         };
     }
 
-    private onRoomStateMember = (ev: MatrixEvent, state: RoomState, member: RoomMember) => {
+    private onRoomStateMember = (ev: MatrixEvent, state: RoomState, member: RoomMember): void => {
         if (!this.props.room || member.roomId !== this.props.room.roomId) {
             return;
         }
@@ -118,11 +118,11 @@ export default class RightPanel extends React.Component<IProps, IState> {
         }
     };
 
-    private onRightPanelStoreUpdate = () => {
+    private onRightPanelStoreUpdate = (): void => {
         this.setState({ ...(RightPanel.getDerivedStateFromProps(this.props) as IState) });
     };
 
-    private onClose = () => {
+    private onClose = (): void => {
         // XXX: There are three different ways of 'closing' this panel depending on what state
         // things are in... this knows far more than it should do about the state of the rest
         // of the app and is generally a bit silly.

src/components/structures/RoomSearch.tsx

@@ -39,15 +39,15 @@ export default class RoomSearch extends React.PureComponent<IProps> {
         this.dispatcherRef = defaultDispatcher.register(this.onAction);
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         defaultDispatcher.unregister(this.dispatcherRef);
     }
 
-    private openSpotlight() {
+    private openSpotlight(): void {
         Modal.createDialog(SpotlightDialog, {}, "mx_SpotlightDialog_wrapper", false, true);
     }
 
-    private onAction = (payload: ActionPayload) => {
+    private onAction = (payload: ActionPayload): void => {
         if (payload.action === "focus_room_filter") {
             this.openSpotlight();
         }

src/components/structures/RoomSearchView.tsx

@@ -37,7 +37,7 @@ import RoomContext from "../../contexts/RoomContext";
 import SettingsStore from "../../settings/SettingsStore";
 
 const DEBUG = false;
-let debuglog = function (msg: string) {};
+let debuglog = function (msg: string): void {};
 
 /* istanbul ignore next */
 if (DEBUG) {
@@ -76,7 +76,7 @@ export const RoomSearchView = forwardRef<ScrollPanel, Props>(
 
                 return searchPromise
                     .then(
-                        async (results) => {
+                        async (results): Promise<boolean> => {
                             debuglog("search complete");
                             if (aborted.current) {
                                 logger.error("Discarding stale search results");
@@ -209,7 +209,7 @@ export const RoomSearchView = forwardRef<ScrollPanel, Props>(
 
         // once dynamic content in the search results load, make the scrollPanel check
         // the scroll offsets.
-        const onHeightChanged = () => {
+        const onHeightChanged = (): void => {
             const scrollPanel = ref.current;
             scrollPanel?.checkScroll();
         };

src/components/structures/RoomStatusBar.tsx

@@ -146,7 +146,7 @@ export default class RoomStatusBar extends React.PureComponent<IProps, IState> {
         dis.fire(Action.FocusSendMessageComposer);
     };
 
-    private onRoomLocalEchoUpdated = (ev: MatrixEvent, room: Room) => {
+    private onRoomLocalEchoUpdated = (ev: MatrixEvent, room: Room): void => {
         if (room.roomId !== this.props.room.roomId) return;
         const messages = getUnsentMessages(this.props.room);
         this.setState({

src/components/structures/RoomView.tsx

@@ -115,7 +115,7 @@ import VoipUserMapper from "../../VoipUserMapper";
 import { isCallEvent } from "./LegacyCallEventGrouper";
 
 const DEBUG = false;
-let debuglog = function (msg: string) {};
+let debuglog = function (msg: string): void {};
 
 const BROWSER_SUPPORTS_SANDBOX = "sandbox" in document.createElement("iframe");
 
@@ -248,7 +248,7 @@ function LocalRoomView(props: LocalRoomViewProps): ReactElement {
         encryptionTile = <EncryptionEvent mxEvent={encryptionEvent} />;
     }
 
-    const onRetryClicked = () => {
+    const onRetryClicked = (): void => {
         room.state = LocalRoomState.NEW;
         defaultDispatcher.dispatch({
             action: "local_room_event",
@@ -470,21 +470,21 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         ];
     }
 
-    private onIsResizing = (resizing: boolean) => {
+    private onIsResizing = (resizing: boolean): void => {
         this.setState({ resizing });
     };
 
-    private onWidgetStoreUpdate = () => {
+    private onWidgetStoreUpdate = (): void => {
         if (!this.state.room) return;
         this.checkWidgets(this.state.room);
     };
 
-    private onWidgetEchoStoreUpdate = () => {
+    private onWidgetEchoStoreUpdate = (): void => {
         if (!this.state.room) return;
         this.checkWidgets(this.state.room);
     };
 
-    private onWidgetLayoutChange = () => {
+    private onWidgetLayoutChange = (): void => {
         if (!this.state.room) return;
         dis.dispatch({
             action: "appsDrawer",
@@ -505,7 +505,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         });
     };
 
-    private getMainSplitContentType = (room: Room) => {
+    private getMainSplitContentType = (room: Room): MainSplitContentType => {
         if (
             (SettingsStore.getValue("feature_group_calls") && this.context.roomViewStore.isViewingCall()) ||
             isVideoRoom(room)
@@ -707,7 +707,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         }
     };
 
-    private onActiveCalls = () => {
+    private onActiveCalls = (): void => {
         if (this.state.roomId === undefined) return;
         const activeCall = CallStore.instance.getActiveCall(this.state.roomId);
 
@@ -727,7 +727,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         this.setState({ activeCall });
     };
 
-    private getRoomId = () => {
+    private getRoomId = (): string => {
         // According to `onRoomViewStoreUpdate`, `state.roomId` can be null
         // if we have a room alias we haven't resolved yet. To work around this,
         // first we'll try the room object if it's there, and then fallback to
@@ -736,7 +736,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         return this.state.room ? this.state.room.roomId : this.state.roomId;
     };
 
-    private getPermalinkCreatorForRoom(room: Room) {
+    private getPermalinkCreatorForRoom(room: Room): RoomPermalinkCreator {
         if (this.permalinkCreators[room.roomId]) return this.permalinkCreators[room.roomId];
 
         this.permalinkCreators[room.roomId] = new RoomPermalinkCreator(room);
@@ -750,14 +750,14 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         return this.permalinkCreators[room.roomId];
     }
 
-    private stopAllPermalinkCreators() {
+    private stopAllPermalinkCreators(): void {
         if (!this.permalinkCreators) return;
         for (const roomId of Object.keys(this.permalinkCreators)) {
             this.permalinkCreators[roomId].stop();
         }
     }
 
-    private setupRoom(room: Room, roomId: string, joining: boolean, shouldPeek: boolean) {
+    private setupRoom(room: Room, roomId: string, joining: boolean, shouldPeek: boolean): void {
         // if this is an unknown room then we're in one of three states:
         // - This is a room we can peek into (search engine) (we can /peek)
         // - This is a room we can publicly join or were invited to. (we can /join)
@@ -822,7 +822,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         }
     }
 
-    private shouldShowApps(room: Room) {
+    private shouldShowApps(room: Room): boolean {
         if (!BROWSER_SUPPORTS_SANDBOX || !room) return false;
 
         // Check if user has previously chosen to hide the app drawer for this
@@ -838,7 +838,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         return isManuallyShown && widgets.length > 0;
     }
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         this.onRoomViewStoreUpdate(true);
 
         const call = this.getCallForRoom();
@@ -851,7 +851,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         window.addEventListener("beforeunload", this.onPageUnload);
     }
 
-    public shouldComponentUpdate(nextProps, nextState) {
+    public shouldComponentUpdate(nextProps, nextState): boolean {
         const hasPropsDiff = objectHasDiff(this.props, nextProps);
 
         const { upgradeRecommendation, ...state } = this.state;
@@ -864,7 +864,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         return hasPropsDiff || hasStateDiff;
     }
 
-    public componentDidUpdate() {
+    public componentDidUpdate(): void {
         // Note: We check the ref here with a flag because componentDidMount, despite
         // documentation, does not define our messagePanel ref. It looks like our spinner
         // in render() prevents the ref from being set on first mount, so we try and
@@ -877,7 +877,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         }
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         // set a boolean to say we've been unmounted, which any pending
         // promises can use to throw away their results.
         //
@@ -947,13 +947,13 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         }
     }
 
-    private onRightPanelStoreUpdate = () => {
+    private onRightPanelStoreUpdate = (): void => {
         this.setState({
             showRightPanel: this.context.rightPanelStore.isOpenForRoom(this.state.roomId),
         });
     };
 
-    private onPageUnload = (event) => {
+    private onPageUnload = (event): string => {
         if (ContentMessages.sharedInstance().getCurrentUploads().length > 0) {
             return (event.returnValue = _t("You seem to be uploading files, are you sure you want to quit?"));
         } else if (this.getCallForRoom() && this.state.callState !== "ended") {
@@ -961,7 +961,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         }
     };
 
-    private onReactKeyDown = (ev) => {
+    private onReactKeyDown = (ev): void => {
         let handled = false;
 
         const action = getKeyBindingsManager().getRoomAction(ev);
@@ -1120,12 +1120,12 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         }
     };
 
-    private onLocalRoomEvent(roomId: string) {
+    private onLocalRoomEvent(roomId: string): void {
         if (roomId !== this.state.room.roomId) return;
         createRoomFromLocalRoom(this.context.client, this.state.room as LocalRoom);
     }
 
-    private onRoomTimeline = (ev: MatrixEvent, room: Room | null, toStartOfTimeline: boolean, removed, data) => {
+    private onRoomTimeline = (ev: MatrixEvent, room: Room | null, toStartOfTimeline: boolean, removed, data): void => {
         if (this.unmounted) return;
 
         // ignore events for other rooms or the notification timeline set
@@ -1167,7 +1167,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         }
     };
 
-    private onEventDecrypted = (ev: MatrixEvent) => {
+    private onEventDecrypted = (ev: MatrixEvent): void => {
         if (!this.state.room || !this.state.matrixClientIsReady) return; // not ready at all
         if (ev.getRoomId() !== this.state.room.roomId) return; // not for us
         this.updateVisibleDecryptionFailures();
@@ -1175,7 +1175,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         this.handleEffects(ev);
     };
 
-    private handleEffects = (ev: MatrixEvent) => {
+    private handleEffects = (ev: MatrixEvent): void => {
         const notifState = this.context.roomNotificationStateStore.getRoomState(this.state.room);
         if (!notifState.isUnread) return;
 
@@ -1189,19 +1189,19 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         });
     };
 
-    private onRoomName = (room: Room) => {
+    private onRoomName = (room: Room): void => {
         if (this.state.room && room.roomId == this.state.room.roomId) {
             this.forceUpdate();
         }
     };
 
-    private onKeyBackupStatus = () => {
+    private onKeyBackupStatus = (): void => {
         // Key backup status changes affect whether the in-room recovery
         // reminder is displayed.
         this.forceUpdate();
     };
 
-    public canResetTimeline = () => {
+    public canResetTimeline = (): boolean => {
         if (!this.messagePanel) {
             return true;
         }
@@ -1216,7 +1216,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
 
     // called when state.room is first initialised (either at initial load,
     // after a successful peek, or after we join the room).
-    private onRoomLoaded = (room: Room) => {
+    private onRoomLoaded = (room: Room): void => {
         if (this.unmounted) return;
         // Attach a widget store listener only when we get a room
         this.context.widgetLayoutStore.on(WidgetLayoutStore.emissionForRoom(room), this.onWidgetLayoutChange);
@@ -1251,17 +1251,17 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         }
     };
 
-    private getRoomTombstone(room = this.state.room) {
+    private getRoomTombstone(room = this.state.room): MatrixEvent | undefined {
         return room?.currentState.getStateEvents(EventType.RoomTombstone, "");
     }
 
-    private async calculateRecommendedVersion(room: Room) {
+    private async calculateRecommendedVersion(room: Room): Promise<void> {
         const upgradeRecommendation = await room.getRecommendedVersion();
         if (this.unmounted) return;
         this.setState({ upgradeRecommendation });
     }
 
-    private async loadMembersIfJoined(room: Room) {
+    private async loadMembersIfJoined(room: Room): Promise<void> {
         // lazy load members if enabled
         if (this.context.client.hasLazyLoadMembersEnabled()) {
             if (room && room.getMyMembership() === "join") {
@@ -1280,14 +1280,14 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         }
     }
 
-    private calculatePeekRules(room: Room) {
+    private calculatePeekRules(room: Room): void {
         const historyVisibility = room.currentState.getStateEvents(EventType.RoomHistoryVisibility, "");
         this.setState({
             canPeek: historyVisibility?.getContent().history_visibility === HistoryVisibility.WorldReadable,
         });
     }
 
-    private updatePreviewUrlVisibility({ roomId }: Room) {
+    private updatePreviewUrlVisibility({ roomId }: Room): void {
         // URL Previews in E2EE rooms can be a privacy leak so use a different setting which is per-room explicit
         const key = this.context.client.isRoomEncrypted(roomId) ? "urlPreviewsEnabled_e2ee" : "urlPreviewsEnabled";
         this.setState({
@@ -1295,7 +1295,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         });
     }
 
-    private onRoom = (room: Room) => {
+    private onRoom = (room: Room): void => {
         if (!room || room.roomId !== this.state.roomId) {
             return;
         }
@@ -1318,7 +1318,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         );
     };
 
-    private onDeviceVerificationChanged = (userId: string) => {
+    private onDeviceVerificationChanged = (userId: string): void => {
         const room = this.state.room;
         if (!room?.currentState.getMember(userId)) {
             return;
@@ -1326,7 +1326,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         this.updateE2EStatus(room);
     };
 
-    private onUserVerificationChanged = (userId: string) => {
+    private onUserVerificationChanged = (userId: string): void => {
         const room = this.state.room;
         if (!room || !room.currentState.getMember(userId)) {
             return;
@@ -1334,14 +1334,14 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         this.updateE2EStatus(room);
     };
 
-    private onCrossSigningKeysChanged = () => {
+    private onCrossSigningKeysChanged = (): void => {
         const room = this.state.room;
         if (room) {
             this.updateE2EStatus(room);
         }
     };
 
-    private async updateE2EStatus(room: Room) {
+    private async updateE2EStatus(room: Room): Promise<void> {
         if (!this.context.client.isRoomEncrypted(room.roomId)) return;
 
         // If crypto is not currently enabled, we aren't tracking devices at all,
@@ -1357,13 +1357,13 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         this.setState({ e2eStatus });
     }
 
-    private onUrlPreviewsEnabledChange = () => {
+    private onUrlPreviewsEnabledChange = (): void => {
         if (this.state.room) {
             this.updatePreviewUrlVisibility(this.state.room);
         }
     };
 
-    private onRoomStateEvents = (ev: MatrixEvent, state: RoomState) => {
+    private onRoomStateEvents = (ev: MatrixEvent, state: RoomState): void => {
         // ignore if we don't have a room yet
         if (!this.state.room || this.state.room.roomId !== state.roomId) return;
 
@@ -1377,7 +1377,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         }
     };
 
-    private onRoomStateUpdate = (state: RoomState) => {
+    private onRoomStateUpdate = (state: RoomState): void => {
         // ignore members in other rooms
         if (state.roomId !== this.state.room?.roomId) {
             return;
@@ -1386,7 +1386,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         this.updateRoomMembers();
     };
 
-    private onMyMembership = (room: Room, membership: string, oldMembership: string) => {
+    private onMyMembership = (room: Room, membership: string, oldMembership: string): void => {
         if (room.roomId === this.state.roomId) {
             this.forceUpdate();
             this.loadMembersIfJoined(room);
@@ -1394,7 +1394,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         }
     };
 
-    private updatePermissions(room: Room) {
+    private updatePermissions(room: Room): void {
         if (room) {
             const me = this.context.client.getUserId();
             const canReact =
@@ -1420,7 +1420,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         { leading: true, trailing: true },
     );
 
-    private checkDesktopNotifications() {
+    private checkDesktopNotifications(): void {
         const memberCount = this.state.room.getJoinedMemberCount() + this.state.room.getInvitedMemberCount();
         // if they are not alone prompt the user about notifications so they don't miss replies
         if (memberCount > 1 && Notifier.shouldShowPrompt()) {
@@ -1428,7 +1428,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         }
     }
 
-    private updateDMState() {
+    private updateDMState(): void {
         const room = this.state.room;
         if (room.getMyMembership() != "join") {
             return;
@@ -1439,7 +1439,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         }
     }
 
-    private onInviteClick = () => {
+    private onInviteClick = (): void => {
         // open the room inviter
         dis.dispatch({
             action: "view_invite",
@@ -1447,7 +1447,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         });
     };
 
-    private onJoinButtonClicked = () => {
+    private onJoinButtonClicked = (): void => {
         // If the user is a ROU, allow them to transition to a PWLU
         if (this.context.client?.isGuest()) {
             // Join this room once the user has registered and logged in
@@ -1489,7 +1489,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         { leading: false, trailing: true },
     );
 
-    private onMessageListScroll = () => {
+    private onMessageListScroll = (): void => {
         if (this.messagePanel.isAtEndOfLiveTimeline()) {
             this.setState({
                 numUnreadMessages: 0,
@@ -1504,7 +1504,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         this.updateVisibleDecryptionFailures();
     };
 
-    private resetJumpToEvent = (eventId?: string) => {
+    private resetJumpToEvent = (eventId?: string): void => {
         if (
             this.state.initialEventId &&
             this.state.initialEventScrollIntoView &&
@@ -1523,7 +1523,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         }
     };
 
-    private injectSticker(url: string, info: object, text: string, threadId: string | null) {
+    private injectSticker(url: string, info: object, text: string, threadId: string | null): void {
         if (this.context.client.isGuest()) {
             dis.dispatch({ action: "require_registration" });
             return;
@@ -1539,7 +1539,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
             });
     }
 
-    private onSearch = (term: string, scope: SearchScope) => {
+    private onSearch = (term: string, scope: SearchScope): void => {
         const roomId = scope === SearchScope.Room ? this.state.room.roomId : undefined;
         debuglog("sending search request");
         const abortController = new AbortController();
@@ -1569,21 +1569,21 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         });
     };
 
-    private onAppsClick = () => {
+    private onAppsClick = (): void => {
         dis.dispatch({
             action: "appsDrawer",
             show: !this.state.showApps,
         });
     };
 
-    private onForgetClick = () => {
+    private onForgetClick = (): void => {
         dis.dispatch({
             action: "forget_room",
             room_id: this.state.room.roomId,
         });
     };
 
-    private onRejectButtonClicked = () => {
+    private onRejectButtonClicked = (): void => {
         this.setState({
             rejecting: true,
         });
@@ -1611,7 +1611,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         );
     };
 
-    private onRejectAndIgnoreClick = async () => {
+    private onRejectAndIgnoreClick = async (): Promise<void> => {
         this.setState({
             rejecting: true,
         });
@@ -1644,7 +1644,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         }
     };
 
-    private onRejectThreepidInviteButtonClicked = () => {
+    private onRejectThreepidInviteButtonClicked = (): void => {
         // We can reject 3pid invites in the same way that we accept them,
         // using /leave rather than /join. In the short term though, we
         // just ignore them.
@@ -1652,7 +1652,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         dis.fire(Action.ViewRoomDirectory);
     };
 
-    private onSearchClick = () => {
+    private onSearchClick = (): void => {
         this.setState({
             timelineRenderingType:
                 this.state.timelineRenderingType === TimelineRenderingType.Search
@@ -1674,7 +1674,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
     };
 
     // jump down to the bottom of this room, where new events are arriving
-    private jumpToLiveTimeline = () => {
+    private jumpToLiveTimeline = (): void => {
         if (this.state.initialEventId && this.state.isInitialEventHighlighted) {
             // If we were viewing a highlighted event, firing view_room without
             // an event will take care of both clearing the URL fragment and
@@ -1692,18 +1692,18 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
     };
 
     // jump up to wherever our read marker is
-    private jumpToReadMarker = () => {
+    private jumpToReadMarker = (): void => {
         this.messagePanel.jumpToReadMarker();
     };
 
     // update the read marker to match the read-receipt
-    private forgetReadMarker = (ev) => {
+    private forgetReadMarker = (ev): void => {
         ev.stopPropagation();
         this.messagePanel.forgetReadMarker();
     };
 
     // decide whether or not the top 'unread messages' bar should be shown
-    private updateTopUnreadMessagesBar = () => {
+    private updateTopUnreadMessagesBar = (): void => {
         if (!this.messagePanel) {
             return;
         }
@@ -1754,12 +1754,12 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         };
     }
 
-    private onStatusBarVisible = () => {
+    private onStatusBarVisible = (): void => {
         if (this.unmounted || this.state.statusBarVisible) return;
         this.setState({ statusBarVisible: true });
     };
 
-    private onStatusBarHidden = () => {
+    private onStatusBarHidden = (): void => {
         // This is currently not desired as it is annoying if it keeps expanding and collapsing
         if (this.unmounted || !this.state.statusBarVisible) return;
         this.setState({ statusBarVisible: false });
@@ -1770,7 +1770,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
      *
      * We pass it down to the scroll panel.
      */
-    public handleScrollKey = (ev) => {
+    public handleScrollKey = (ev): void => {
         let panel: ScrollPanel | TimelinePanel;
         if (this.searchResultsPanel.current) {
             panel = this.searchResultsPanel.current;
@@ -1793,24 +1793,24 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
 
     // this has to be a proper method rather than an unnamed function,
     // otherwise react calls it with null on each update.
-    private gatherTimelinePanelRef = (r) => {
+    private gatherTimelinePanelRef = (r): void => {
         this.messagePanel = r;
     };
 
-    private getOldRoom() {
+    private getOldRoom(): Room | null {
         const createEvent = this.state.room.currentState.getStateEvents(EventType.RoomCreate, "");
         if (!createEvent || !createEvent.getContent()["predecessor"]) return null;
 
         return this.context.client.getRoom(createEvent.getContent()["predecessor"]["room_id"]);
     }
 
-    public getHiddenHighlightCount() {
+    public getHiddenHighlightCount(): number {
         const oldRoom = this.getOldRoom();
         if (!oldRoom) return 0;
         return oldRoom.getUnreadNotificationCount(NotificationCountType.Highlight);
     }
 
-    public onHiddenHighlightsClick = () => {
+    public onHiddenHighlightsClick = (): void => {
         const oldRoom = this.getOldRoom();
         if (!oldRoom) return;
         dis.dispatch<ViewRoomPayload>({
@@ -1826,7 +1826,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         });
     }
 
-    private onFileDrop = (dataTransfer: DataTransfer) =>
+    private onFileDrop = (dataTransfer: DataTransfer): Promise<void> =>
         ContentMessages.sharedInstance().sendContentListToRoom(
             Array.from(dataTransfer.files),
             this.state.room?.roomId ?? this.state.roomId,
@@ -1869,7 +1869,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         );
     }
 
-    public render() {
+    public render(): JSX.Element {
         if (this.state.room instanceof LocalRoom) {
             if (this.state.room.state === LocalRoomState.CREATING) {
                 return this.renderLocalRoomCreateLoader();

src/components/structures/ScrollPanel.tsx

@@ -35,7 +35,7 @@ const UNFILL_REQUEST_DEBOUNCE_MS = 200;
 // much while the content loads.
 const PAGE_SIZE = 400;
 
-const debuglog = (...args: any[]) => {
+const debuglog = (...args: any[]): void => {
     if (SettingsStore.getValue("debug_scroll_panel")) {
         logger.log.call(console, "ScrollPanel debuglog:", ...args);
     }
@@ -227,14 +227,14 @@ export default class ScrollPanel extends React.Component<IProps> {
         this.props.resizeNotifier?.removeListener("middlePanelResizedNoisy", this.onResize);
     }
 
-    private onScroll = (ev: Event | React.UIEvent): void => {
+    private onScroll = (ev: Event): void => {
         // skip scroll events caused by resizing
         if (this.props.resizeNotifier && this.props.resizeNotifier.isResizing) return;
         debuglog("onScroll called past resize gate; scroll node top:", this.getScrollNode().scrollTop);
         this.scrollTimeout.restart();
         this.saveScrollState();
         this.updatePreventShrinking();
-        this.props.onScroll?.(ev as Event);
+        this.props.onScroll?.(ev);
         // noinspection JSIgnoredPromiseFromCall
         this.checkFillState();
     };
@@ -587,7 +587,7 @@ export default class ScrollPanel extends React.Component<IProps> {
      * Scroll up/down in response to a scroll key
      * @param {object} ev the keyboard event
      */
-    public handleScrollKey = (ev: KeyboardEvent) => {
+    public handleScrollKey = (ev: KeyboardEvent): void => {
         const roomAction = getKeyBindingsManager().getRoomAction(ev);
         switch (roomAction) {
             case KeyBindingAction.ScrollUp:
@@ -853,7 +853,7 @@ export default class ScrollPanel extends React.Component<IProps> {
         return this.divScroll;
     }
 
-    private collectScroll = (divScroll: HTMLDivElement) => {
+    private collectScroll = (divScroll: HTMLDivElement): void => {
         this.divScroll = divScroll;
     };
 

src/components/structures/SpaceHierarchy.tsx

@@ -114,12 +114,12 @@ const Tile: React.FC<ITileProps> = ({
     const [onFocus, isActive, ref] = useRovingTabIndex();
     const [busy, setBusy] = useState(false);
 
-    const onPreviewClick = (ev: ButtonEvent) => {
+    const onPreviewClick = (ev: ButtonEvent): void => {
         ev.preventDefault();
         ev.stopPropagation();
         onViewRoomClick();
     };
-    const onJoinClick = async (ev: ButtonEvent) => {
+    const onJoinClick = async (ev: ButtonEvent): Promise<void> => {
         setBusy(true);
         ev.preventDefault();
         ev.stopPropagation();
@@ -271,7 +271,7 @@ const Tile: React.FC<ITileProps> = ({
         );
 
         if (showChildren) {
-            const onChildrenKeyDown = (e) => {
+            const onChildrenKeyDown = (e): void => {
                 const action = getKeyBindingsManager().getAccessibilityAction(e);
                 switch (action) {
                     case KeyBindingAction.ArrowLeft:
@@ -439,7 +439,7 @@ const toLocalRoom = (cli: MatrixClient, room: IHierarchyRoom): IHierarchyRoom =>
     return room;
 };
 
-export const HierarchyLevel = ({
+export const HierarchyLevel: React.FC<IHierarchyLevelProps> = ({
     root,
     roomSet,
     hierarchy,
@@ -448,7 +448,7 @@ export const HierarchyLevel = ({
     onViewRoomClick,
     onJoinRoomClick,
     onToggleClick,
-}: IHierarchyLevelProps) => {
+}) => {
     const cli = useContext(MatrixClientContext);
     const space = cli.getRoom(root.room_id);
     const hasPermissions = space?.currentState.maySendStateEvent(EventType.SpaceChild, cli.getUserId());
@@ -553,7 +553,7 @@ export const useRoomHierarchy = (
     });
 
     const loadMore = useCallback(
-        async (pageSize?: number) => {
+        async (pageSize?: number): Promise<void> => {
             if (hierarchy.loading || !hierarchy.canLoadMore || hierarchy.noSupport || error) return;
             await hierarchy.load(pageSize).catch(setError);
             setRooms(hierarchy.rooms);
@@ -578,8 +578,8 @@ export const useRoomHierarchy = (
     };
 };
 
-const useIntersectionObserver = (callback: () => void) => {
-    const handleObserver = (entries: IntersectionObserverEntry[]) => {
+const useIntersectionObserver = (callback: () => void): ((element: HTMLDivElement) => void) => {
+    const handleObserver = (entries: IntersectionObserverEntry[]): void => {
         const target = entries[0];
         if (target.isIntersecting) {
             callback();
@@ -610,7 +610,7 @@ interface IManageButtonsProps {
     setError: Dispatch<SetStateAction<string>>;
 }
 
-const ManageButtons = ({ hierarchy, selected, setSelected, setError }: IManageButtonsProps) => {
+const ManageButtons: React.FC<IManageButtonsProps> = ({ hierarchy, selected, setSelected, setError }) => {
     const cli = useContext(MatrixClientContext);
 
     const [removing, setRemoving] = useState(false);
@@ -645,7 +645,7 @@ const ManageButtons = ({ hierarchy, selected, setSelected, setError }: IManageBu
         <>
             <Button
                 {...props}
-                onClick={async () => {
+                onClick={async (): Promise<void> => {
                     setRemoving(true);
                     try {
                         const userId = cli.getUserId();
@@ -680,7 +680,7 @@ const ManageButtons = ({ hierarchy, selected, setSelected, setError }: IManageBu
             </Button>
             <Button
                 {...props}
-                onClick={async () => {
+                onClick={async (): Promise<void> => {
                     setSaving(true);
                     try {
                         for (const [parentId, childId] of selectedRelations) {
@@ -713,7 +713,7 @@ const ManageButtons = ({ hierarchy, selected, setSelected, setError }: IManageBu
     );
 };
 
-const SpaceHierarchy = ({ space, initialText = "", showRoom, additionalButtons }: IProps) => {
+const SpaceHierarchy: React.FC<IProps> = ({ space, initialText = "", showRoom, additionalButtons }) => {
     const cli = useContext(MatrixClientContext);
     const [query, setQuery] = useState(initialText);
 

src/components/structures/SpaceRoomView.tsx

@@ -103,7 +103,7 @@ enum Phase {
     PrivateExistingRooms,
 }
 
-const SpaceLandingAddButton = ({ space }) => {
+const SpaceLandingAddButton: React.FC<{ space: Room }> = ({ space }) => {
     const [menuDisplayed, handle, openMenu, closeMenu] = useContextMenu();
     const canCreateRoom = shouldShowComponent(UIComponent.CreateRooms);
     const canCreateSpace = shouldShowComponent(UIComponent.CreateSpaces);
@@ -128,7 +128,7 @@ const SpaceLandingAddButton = ({ space }) => {
                             <IconizedContextMenuOption
                                 label={_t("New room")}
                                 iconClassName="mx_RoomList_iconNewRoom"
-                                onClick={async (e) => {
+                                onClick={async (e): Promise<void> => {
                                     e.preventDefault();
                                     e.stopPropagation();
                                     closeMenu();
@@ -143,7 +143,7 @@ const SpaceLandingAddButton = ({ space }) => {
                                 <IconizedContextMenuOption
                                     label={_t("New video room")}
                                     iconClassName="mx_RoomList_iconNewVideoRoom"
-                                    onClick={async (e) => {
+                                    onClick={async (e): Promise<void> => {
                                         e.preventDefault();
                                         e.stopPropagation();
                                         closeMenu();
@@ -210,7 +210,7 @@ const SpaceLandingAddButton = ({ space }) => {
     );
 };
 
-const SpaceLanding = ({ space }: { space: Room }) => {
+const SpaceLanding: React.FC<{ space: Room }> = ({ space }) => {
     const cli = useContext(MatrixClientContext);
     const myMembership = useMyRoomMembership(space);
     const userId = cli.getUserId();
@@ -259,7 +259,7 @@ const SpaceLanding = ({ space }: { space: Room }) => {
         );
     }
 
-    const onMembersClick = () => {
+    const onMembersClick = (): void => {
         RightPanelStore.instance.setCard({ phase: RightPanelPhases.SpaceMemberList });
     };
 
@@ -297,7 +297,12 @@ const SpaceLanding = ({ space }: { space: Room }) => {
     );
 };
 
-const SpaceSetupFirstRooms = ({ space, title, description, onFinished }) => {
+const SpaceSetupFirstRooms: React.FC<{
+    space: Room;
+    title: string;
+    description: JSX.Element;
+    onFinished(firstRoomId?: string): void;
+}> = ({ space, title, description, onFinished }) => {
     const [busy, setBusy] = useState(false);
     const [error, setError] = useState("");
     const numFields = 3;
@@ -321,7 +326,7 @@ const SpaceSetupFirstRooms = ({ space, title, description, onFinished }) => {
         );
     });
 
-    const onNextClick = async (ev: ButtonEvent) => {
+    const onNextClick = async (ev: ButtonEvent): Promise<void> => {
         ev.preventDefault();
         if (busy) return;
         setError("");
@@ -354,7 +359,7 @@ const SpaceSetupFirstRooms = ({ space, title, description, onFinished }) => {
         setBusy(false);
     };
 
-    let onClick = (ev: ButtonEvent) => {
+    let onClick = (ev: ButtonEvent): void => {
         ev.preventDefault();
         onFinished();
     };
@@ -389,7 +394,10 @@ const SpaceSetupFirstRooms = ({ space, title, description, onFinished }) => {
     );
 };
 
-const SpaceAddExistingRooms = ({ space, onFinished }) => {
+const SpaceAddExistingRooms: React.FC<{
+    space: Room;
+    onFinished(): void;
+}> = ({ space, onFinished }) => {
     return (
         <div>
             <h1>{_t("What do you want to organise?")}</h1>
@@ -420,7 +428,12 @@ interface ISpaceSetupPublicShareProps extends Pick<IProps & IState, "justCreated
     onFinished(): void;
 }
 
-const SpaceSetupPublicShare = ({ justCreatedOpts, space, onFinished, firstRoomId }: ISpaceSetupPublicShareProps) => {
+const SpaceSetupPublicShare: React.FC<ISpaceSetupPublicShareProps> = ({
+    justCreatedOpts,
+    space,
+    onFinished,
+    firstRoomId,
+}) => {
     return (
         <div className="mx_SpaceRoomView_publicShare">
             <h1>
@@ -443,7 +456,11 @@ const SpaceSetupPublicShare = ({ justCreatedOpts, space, onFinished, firstRoomId
     );
 };
 
-const SpaceSetupPrivateScope = ({ space, justCreatedOpts, onFinished }) => {
+const SpaceSetupPrivateScope: React.FC<{
+    space: Room;
+    justCreatedOpts: IOpts;
+    onFinished(createRooms: boolean): void;
+}> = ({ space, justCreatedOpts, onFinished }) => {
     return (
         <div className="mx_SpaceRoomView_privateScope">
             <h1>{_t("Who are you working with?")}</h1>
@@ -485,7 +502,10 @@ const validateEmailRules = withValidation({
     ],
 });
 
-const SpaceSetupPrivateInvite = ({ space, onFinished }) => {
+const SpaceSetupPrivateInvite: React.FC<{
+    space: Room;
+    onFinished(): void;
+}> = ({ space, onFinished }) => {
     const [busy, setBusy] = useState(false);
     const [error, setError] = useState("");
     const numFields = 3;
@@ -501,7 +521,7 @@ const SpaceSetupPrivateInvite = ({ space, onFinished }) => {
                 label={_t("Email address")}
                 placeholder={_t("Email")}
                 value={emailAddresses[i]}
-                onChange={(ev) => setEmailAddress(i, ev.target.value)}
+                onChange={(ev: React.ChangeEvent<HTMLInputElement>) => setEmailAddress(i, ev.target.value)}
                 ref={fieldRefs[i]}
                 onValidate={validateEmailRules}
                 autoFocus={i === 0}
@@ -510,7 +530,7 @@ const SpaceSetupPrivateInvite = ({ space, onFinished }) => {
         );
     });
 
-    const onNextClick = async (ev) => {
+    const onNextClick = async (ev: ButtonEvent): Promise<void> => {
         ev.preventDefault();
         if (busy) return;
         setError("");
@@ -548,7 +568,7 @@ const SpaceSetupPrivateInvite = ({ space, onFinished }) => {
         setBusy(false);
     };
 
-    let onClick = (ev) => {
+    let onClick = (ev: ButtonEvent): void => {
         ev.preventDefault();
         onFinished();
     };
@@ -642,29 +662,29 @@ export default class SpaceRoomView extends React.PureComponent<IProps, IState> {
         RightPanelStore.instance.on(UPDATE_EVENT, this.onRightPanelStoreUpdate);
     }
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         this.context.on(RoomEvent.MyMembership, this.onMyMembership);
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         defaultDispatcher.unregister(this.dispatcherRef);
         RightPanelStore.instance.off(UPDATE_EVENT, this.onRightPanelStoreUpdate);
         this.context.off(RoomEvent.MyMembership, this.onMyMembership);
     }
 
-    private onMyMembership = (room: Room, myMembership: string) => {
+    private onMyMembership = (room: Room, myMembership: string): void => {
         if (room.roomId === this.props.space.roomId) {
             this.setState({ myMembership });
         }
     };
 
-    private onRightPanelStoreUpdate = () => {
+    private onRightPanelStoreUpdate = (): void => {
         this.setState({
             showRightPanel: RightPanelStore.instance.isOpenForRoom(this.props.space.roomId),
         });
     };
 
-    private onAction = (payload: ActionPayload) => {
+    private onAction = (payload: ActionPayload): void => {
         if (payload.action === Action.ViewRoom && payload.room_id === this.props.space.roomId) {
             this.setState({ phase: Phase.Landing });
             return;
@@ -698,7 +718,7 @@ export default class SpaceRoomView extends React.PureComponent<IProps, IState> {
         }
     };
 
-    private goToFirstRoom = async () => {
+    private goToFirstRoom = async (): Promise<void> => {
         if (this.state.firstRoomId) {
             defaultDispatcher.dispatch<ViewRoomPayload>({
                 action: Action.ViewRoom,
@@ -711,7 +731,7 @@ export default class SpaceRoomView extends React.PureComponent<IProps, IState> {
         this.setState({ phase: Phase.Landing });
     };
 
-    private renderBody() {
+    private renderBody(): JSX.Element {
         switch (this.state.phase) {
             case Phase.Landing:
                 if (this.state.myMembership === "join") {
@@ -794,7 +814,7 @@ export default class SpaceRoomView extends React.PureComponent<IProps, IState> {
         }
     }
 
-    public render() {
+    public render(): JSX.Element {
         const rightPanel =
             this.state.showRightPanel && this.state.phase === Phase.Landing ? (
                 <RightPanel room={this.props.space} resizeNotifier={this.props.resizeNotifier} />

src/components/structures/SplashPage.tsx

@@ -19,7 +19,7 @@ interface Props extends DetailedHTMLProps<HTMLAttributes<HTMLElement>, HTMLEleme
     children?: ReactNode;
 }
 
-export default function SplashPage({ children, className, ...other }: Props) {
+export default function SplashPage({ children, className, ...other }: Props): JSX.Element {
     const classes = classNames(className, "mx_SplashPage");
     return (
         <main {...other} className={classes}>

src/components/structures/TabbedView.tsx

@@ -86,7 +86,7 @@ export default class TabbedView extends React.Component<IProps, IState> {
      * @param {Tab} tab the tab to show
      * @private
      */
-    private setActiveTab(tab: Tab) {
+    private setActiveTab(tab: Tab): void {
         // make sure this tab is still in available tabs
         if (!!this.getTabById(tab.id)) {
             if (this.props.onChange) this.props.onChange(tab.id);
@@ -96,7 +96,7 @@ export default class TabbedView extends React.Component<IProps, IState> {
         }
     }
 
-    private renderTabLabel(tab: Tab) {
+    private renderTabLabel(tab: Tab): JSX.Element {
         let classes = "mx_TabbedView_tabLabel ";
 
         if (this.state.activeTabId === tab.id) classes += "mx_TabbedView_tabLabel_active";
@@ -106,7 +106,7 @@ export default class TabbedView extends React.Component<IProps, IState> {
             tabIcon = <span className={`mx_TabbedView_maskedIcon ${tab.icon}`} />;
         }
 
-        const onClickHandler = () => this.setActiveTab(tab);
+        const onClickHandler = (): void => this.setActiveTab(tab);
 
         const label = _t(tab.label);
         return (

src/components/structures/ThreadPanel.tsx

@@ -61,15 +61,12 @@ type ThreadPanelHeaderOption = {
     key: ThreadFilterType;
 };
 
-export const ThreadPanelHeaderFilterOptionItem = ({
-    label,
-    description,
-    onClick,
-    isSelected,
-}: ThreadPanelHeaderOption & {
-    onClick: () => void;
-    isSelected: boolean;
-}) => {
+export const ThreadPanelHeaderFilterOptionItem: React.FC<
+    ThreadPanelHeaderOption & {
+        onClick: () => void;
+        isSelected: boolean;
+    }
+> = ({ label, description, onClick, isSelected }) => {
     return (
         <MenuItemRadio active={isSelected} className="mx_ThreadPanel_Header_FilterOptionItem" onClick={onClick}>
             <span>{label}</span>
@@ -78,15 +75,11 @@ export const ThreadPanelHeaderFilterOptionItem = ({
     );
 };
 
-export const ThreadPanelHeader = ({
-    filterOption,
-    setFilterOption,
-    empty,
-}: {
+export const ThreadPanelHeader: React.FC<{
     filterOption: ThreadFilterType;
     setFilterOption: (filterOption: ThreadFilterType) => void;
     empty: boolean;
-}) => {
+}> = ({ filterOption, setFilterOption, empty }) => {
     const [menuDisplayed, button, openMenu, closeMenu] = useContextMenu<HTMLElement>();
     const options: readonly ThreadPanelHeaderOption[] = [
         {

src/components/structures/ThreadView.tsx

@@ -137,7 +137,7 @@ export default class ThreadView extends React.Component<IProps, IState> {
         });
     }
 
-    public componentDidUpdate(prevProps) {
+    public componentDidUpdate(prevProps): void {
         if (prevProps.mxEvent !== this.props.mxEvent) {
             this.setupThread(this.props.mxEvent);
         }
@@ -192,7 +192,7 @@ export default class ThreadView extends React.Component<IProps, IState> {
         }
     };
 
-    private setupThread = (mxEv: MatrixEvent) => {
+    private setupThread = (mxEv: MatrixEvent): void => {
         let thread = this.props.room.getThread(mxEv.getId());
         if (!thread) {
             thread = this.props.room.createThread(mxEv.getId(), mxEv, [mxEv], true);
@@ -200,7 +200,7 @@ export default class ThreadView extends React.Component<IProps, IState> {
         this.updateThread(thread);
     };
 
-    private onNewThread = (thread: Thread) => {
+    private onNewThread = (thread: Thread): void => {
         if (thread.id === this.props.mxEvent.getId()) {
             this.setupThread(this.props.mxEvent);
         }
@@ -218,7 +218,7 @@ export default class ThreadView extends React.Component<IProps, IState> {
         });
     }
 
-    private updateThread = (thread?: Thread) => {
+    private updateThread = (thread?: Thread): void => {
         if (this.state.thread === thread) return;
 
         this.setupThreadListeners(thread, this.state.thread);
@@ -276,7 +276,7 @@ export default class ThreadView extends React.Component<IProps, IState> {
         this.setState({ narrow });
     };
 
-    private onKeyDown = (ev: KeyboardEvent) => {
+    private onKeyDown = (ev: KeyboardEvent): void => {
         let handled = false;
 
         const action = getKeyBindingsManager().getRoomAction(ev);
@@ -300,7 +300,7 @@ export default class ThreadView extends React.Component<IProps, IState> {
         }
     };
 
-    private onFileDrop = (dataTransfer: DataTransfer) => {
+    private onFileDrop = (dataTransfer: DataTransfer): void => {
         const roomId = this.props.mxEvent.getRoomId();
         if (roomId) {
             ContentMessages.sharedInstance().sendContentListToRoom(

src/components/structures/TimelinePanel.tsx

@@ -31,6 +31,7 @@ import { Thread, ThreadEvent } from "matrix-js-sdk/src/models/thread";
 import { ReceiptType } from "matrix-js-sdk/src/@types/read_receipts";
 import { MatrixError } from "matrix-js-sdk/src/http-api";
 import { ReadReceipt } from "matrix-js-sdk/src/models/read-receipt";
+import { Relations } from "matrix-js-sdk/src/models/relations";
 
 import SettingsStore from "../../settings/SettingsStore";
 import { Layout } from "../../settings/enums/Layout";
@@ -67,7 +68,7 @@ const READ_MARKER_DEBOUNCE_MS = 100;
 // How far off-screen a decryption failure can be for it to still count as "visible"
 const VISIBLE_DECRYPTION_FAILURE_MARGIN = 100;
 
-const debuglog = (...args: any[]) => {
+const debuglog = (...args: any[]): void => {
     if (SettingsStore.getValue("debug_timeline_panel")) {
         logger.log.call(console, "TimelinePanel debuglog:", ...args);
     }
@@ -315,7 +316,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
         this.props.timelineSet.room?.on(ThreadEvent.Update, this.onThreadUpdate);
     }
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         if (this.props.manageReadReceipts) {
             this.updateReadReceiptOnUserActivity();
         }
@@ -325,7 +326,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
         this.initTimeline(this.props);
     }
 
-    public componentDidUpdate(prevProps) {
+    public componentDidUpdate(prevProps: Readonly<IProps>): void {
         if (prevProps.timelineSet !== this.props.timelineSet) {
             // throw new Error("changing timelineSet on a TimelinePanel is not supported");
 
@@ -360,7 +361,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
         }
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         // set a boolean to say we've been unmounted, which any pending
         // promises can use to throw away their results.
         //
@@ -616,7 +617,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
         });
     };
 
-    private onMessageListScroll = (e) => {
+    private onMessageListScroll = (e: Event): void => {
         this.props.onScroll?.(e);
         if (this.props.manageReadMarkers) {
             this.doManageReadMarkers();
@@ -777,7 +778,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
         }
     };
 
-    public canResetTimeline = () => this.messagePanel?.current?.isAtBottom();
+    public canResetTimeline = (): boolean => this.messagePanel?.current?.isAtBottom();
 
     private onRoomRedaction = (ev: MatrixEvent, room: Room): void => {
         if (this.unmounted) return;
@@ -1060,7 +1061,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
                     this.state.readMarkerEventId ?? "",
                     sendRRs ? lastReadEvent ?? undefined : undefined, // Public read receipt (could be null)
                     lastReadEvent ?? undefined, // Private read receipt (could be null)
-                ).catch(async (e) => {
+                ).catch(async (e): Promise<void> => {
                     // /read_markers API is not implemented on this HS, fallback to just RR
                     if (e.errcode === "M_UNRECOGNIZED" && lastReadEvent) {
                         if (
@@ -1070,10 +1071,11 @@ class TimelinePanel extends React.Component<IProps, IState> {
                         )
                             return;
                         try {
-                            return await cli.sendReadReceipt(
+                            await cli.sendReadReceipt(
                                 lastReadEvent,
                                 sendRRs ? ReceiptType.Read : ReceiptType.ReadPrivate,
                             );
+                            return;
                         } catch (error) {
                             logger.error(e);
                             this.lastRRSentEventId = undefined;
@@ -1314,7 +1316,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
      *
      * We pass it down to the scroll panel.
      */
-    public handleScrollKey = (ev) => {
+    public handleScrollKey = (ev: React.KeyboardEvent): void => {
         if (!this.messagePanel.current) return;
 
         // jump to the live timeline on ctrl-end, rather than the end of the
@@ -1342,7 +1344,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
     }
 
     private scrollIntoView(eventId?: string, pixelOffset?: number, offsetBase?: number): void {
-        const doScroll = () => {
+        const doScroll = (): void => {
             if (!this.messagePanel.current) return;
             if (eventId) {
                 debuglog(
@@ -1401,7 +1403,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
             ? new TimelineWindow(cli, this.props.overlayTimelineSet, { windowLimit: this.props.timelineCap })
             : undefined;
 
-        const onLoaded = () => {
+        const onLoaded = (): void => {
             if (this.unmounted) return;
 
             // clear the timeline min-height when (re)loading the timeline
@@ -1441,7 +1443,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
             );
         };
 
-        const onError = (error: MatrixError) => {
+        const onError = (error: MatrixError): void => {
             if (this.unmounted) return;
 
             this.setState({ timelineLoading: false });
@@ -1504,7 +1506,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
             return;
         }
 
-        const prom = this.timelineWindow.load(eventId, INITIAL_SIZE).then(async () => {
+        const prom = this.timelineWindow.load(eventId, INITIAL_SIZE).then(async (): Promise<void> => {
             if (this.overlayTimelineWindow) {
                 // @TODO(kerrya) use timestampToEvent to load the overlay timeline
                 // with more correct position when main TL eventId is truthy
@@ -1746,7 +1748,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
         const wrapperRect = messagePanelNode.getBoundingClientRect();
         const myUserId = MatrixClientPeg.get().credentials.userId;
 
-        const isNodeInView = (node: HTMLElement) => {
+        const isNodeInView = (node: HTMLElement): boolean => {
             if (node) {
                 const boundingRect = node.getBoundingClientRect();
                 if (
@@ -1877,13 +1879,14 @@ class TimelinePanel extends React.Component<IProps, IState> {
         eventId: string,
         relationType: RelationType | string,
         eventType: EventType | string,
-    ) => this.props.timelineSet.relations?.getChildEventsForEvent(eventId, relationType, eventType);
+    ): Relations | undefined =>
+        this.props.timelineSet.relations?.getChildEventsForEvent(eventId, relationType, eventType);
 
     private buildLegacyCallEventGroupers(events?: MatrixEvent[]): void {
         this.callEventGroupers = buildLegacyCallEventGroupers(this.callEventGroupers, events);
     }
 
-    public render() {
+    public render(): JSX.Element {
         // just show a spinner while the timeline loads.
         //
         // put it in a div of the right class (mx_RoomView_messagePanel) so

src/components/structures/ToastContainer.tsx

@@ -39,18 +39,18 @@ export default class ToastContainer extends React.Component<{}, IState> {
         ToastStore.sharedInstance().on("update", this.onToastStoreUpdate);
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         ToastStore.sharedInstance().removeListener("update", this.onToastStoreUpdate);
     }
 
-    private onToastStoreUpdate = () => {
+    private onToastStoreUpdate = (): void => {
         this.setState({
             toasts: ToastStore.sharedInstance().getToasts(),
             countSeen: ToastStore.sharedInstance().getCountSeen(),
         });
     };
 
-    public render() {
+    public render(): JSX.Element {
         const totalCount = this.state.toasts.length;
         const isStacked = totalCount > 1;
         let toast;

src/components/structures/UploadBar.tsx

@@ -65,12 +65,12 @@ export default class UploadBar extends React.PureComponent<IProps, IState> {
         this.state = this.calculateState();
     }
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         this.dispatcherRef = dis.register(this.onAction);
         this.mounted = true;
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         this.mounted = false;
         dis.unregister(this.dispatcherRef!);
     }
@@ -91,19 +91,19 @@ export default class UploadBar extends React.PureComponent<IProps, IState> {
         };
     }
 
-    private onAction = (payload: ActionPayload) => {
+    private onAction = (payload: ActionPayload): void => {
         if (!this.mounted) return;
         if (isUploadPayload(payload)) {
             this.setState(this.calculateState());
         }
     };
 
-    private onCancelClick = (ev: ButtonEvent) => {
+    private onCancelClick = (ev: ButtonEvent): void => {
         ev.preventDefault();
         ContentMessages.sharedInstance().cancelUpload(this.state.currentUpload!);
     };
 
-    public render() {
+    public render(): JSX.Element {
         if (!this.state.currentFile) {
             return null;
         }

src/components/structures/UserMenu.tsx

@@ -22,7 +22,7 @@ import defaultDispatcher from "../../dispatcher/dispatcher";
 import { ActionPayload } from "../../dispatcher/payloads";
 import { Action } from "../../dispatcher/actions";
 import { _t } from "../../languageHandler";
-import { ChevronFace, ContextMenuButton } from "./ContextMenu";
+import { ChevronFace, ContextMenuButton, MenuProps } from "./ContextMenu";
 import { UserTab } from "../views/dialogs/UserTab";
 import { OpenToTabPayload } from "../../dispatcher/payloads/OpenToTabPayload";
 import FeedbackDialog from "../views/dialogs/FeedbackDialog";
@@ -67,7 +67,7 @@ interface IState {
     showLiveAvatarAddon: boolean;
 }
 
-const toRightOf = (rect: PartialDOMRect) => {
+const toRightOf = (rect: PartialDOMRect): MenuProps => {
     return {
         left: rect.width + rect.left + 8,
         top: rect.top,
@@ -75,7 +75,7 @@ const toRightOf = (rect: PartialDOMRect) => {
     };
 };
 
-const below = (rect: PartialDOMRect) => {
+const below = (rect: PartialDOMRect): MenuProps => {
     return {
         left: rect.left,
         top: rect.top + rect.height,
@@ -118,7 +118,7 @@ export default class UserMenu extends React.Component<IProps, IState> {
         });
     };
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         this.context.voiceBroadcastRecordingsStore.on(
             VoiceBroadcastRecordingsStoreEvent.CurrentChanged,
             this.onCurrentVoiceBroadcastRecordingChanged,
@@ -127,7 +127,7 @@ export default class UserMenu extends React.Component<IProps, IState> {
         this.themeWatcherRef = SettingsStore.watchSetting("theme", null, this.onThemeChanged);
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         if (this.themeWatcherRef) SettingsStore.unwatchSetting(this.themeWatcherRef);
         if (this.dndWatcherRef) SettingsStore.unwatchSetting(this.dndWatcherRef);
         if (this.dispatcherRef) defaultDispatcher.unregister(this.dispatcherRef);
@@ -163,26 +163,26 @@ export default class UserMenu extends React.Component<IProps, IState> {
         }
     }
 
-    private onProfileUpdate = async () => {
+    private onProfileUpdate = async (): Promise<void> => {
         // the store triggered an update, so force a layout update. We don't
         // have any state to store here for that to magically happen.
         this.forceUpdate();
     };
 
-    private onSelectedSpaceUpdate = async () => {
+    private onSelectedSpaceUpdate = async (): Promise<void> => {
         this.setState({
             selectedSpace: SpaceStore.instance.activeSpaceRoom,
         });
     };
 
-    private onThemeChanged = () => {
+    private onThemeChanged = (): void => {
         this.setState({
             isDarkTheme: this.isUserOnDarkTheme(),
             isHighContrast: this.isUserOnHighContrastTheme(),
         });
     };
 
-    private onAction = (payload: ActionPayload) => {
+    private onAction = (payload: ActionPayload): void => {
         switch (payload.action) {
             case Action.ToggleUserMenu:
                 if (this.state.contextMenuPosition) {
@@ -194,13 +194,13 @@ export default class UserMenu extends React.Component<IProps, IState> {
         }
     };
 
-    private onOpenMenuClick = (ev: React.MouseEvent) => {
+    private onOpenMenuClick = (ev: React.MouseEvent): void => {
         ev.preventDefault();
         ev.stopPropagation();
         this.setState({ contextMenuPosition: ev.currentTarget.getBoundingClientRect() });
     };
 
-    private onContextMenu = (ev: React.MouseEvent) => {
+    private onContextMenu = (ev: React.MouseEvent): void => {
         ev.preventDefault();
         ev.stopPropagation();
         this.setState({
@@ -213,11 +213,11 @@ export default class UserMenu extends React.Component<IProps, IState> {
         });
     };
 
-    private onCloseMenu = () => {
+    private onCloseMenu = (): void => {
         this.setState({ contextMenuPosition: null });
     };
 
-    private onSwitchThemeClick = (ev: React.MouseEvent) => {
+    private onSwitchThemeClick = (ev: React.MouseEvent): void => {
         ev.preventDefault();
         ev.stopPropagation();
 
@@ -236,7 +236,7 @@ export default class UserMenu extends React.Component<IProps, IState> {
         SettingsStore.setValue("theme", null, SettingLevel.DEVICE, newTheme); // set at same level as Appearance tab
     };
 
-    private onSettingsOpen = (ev: ButtonEvent, tabId: string) => {
+    private onSettingsOpen = (ev: ButtonEvent, tabId: string): void => {
         ev.preventDefault();
         ev.stopPropagation();
 
@@ -245,7 +245,7 @@ export default class UserMenu extends React.Component<IProps, IState> {
         this.setState({ contextMenuPosition: null }); // also close the menu
     };
 
-    private onProvideFeedback = (ev: ButtonEvent) => {
+    private onProvideFeedback = (ev: ButtonEvent): void => {
         ev.preventDefault();
         ev.stopPropagation();
 
@@ -253,7 +253,7 @@ export default class UserMenu extends React.Component<IProps, IState> {
         this.setState({ contextMenuPosition: null }); // also close the menu
     };
 
-    private onSignOutClick = async (ev: ButtonEvent) => {
+    private onSignOutClick = async (ev: ButtonEvent): Promise<void> => {
         ev.preventDefault();
         ev.stopPropagation();
 
@@ -268,17 +268,17 @@ export default class UserMenu extends React.Component<IProps, IState> {
         this.setState({ contextMenuPosition: null }); // also close the menu
     };
 
-    private onSignInClick = () => {
+    private onSignInClick = (): void => {
         defaultDispatcher.dispatch({ action: "start_login" });
         this.setState({ contextMenuPosition: null }); // also close the menu
     };
 
-    private onRegisterClick = () => {
+    private onRegisterClick = (): void => {
         defaultDispatcher.dispatch({ action: "start_registration" });
         this.setState({ contextMenuPosition: null }); // also close the menu
     };
 
-    private onHomeClick = (ev: ButtonEvent) => {
+    private onHomeClick = (ev: ButtonEvent): void => {
         ev.preventDefault();
         ev.stopPropagation();
 
@@ -429,7 +429,7 @@ export default class UserMenu extends React.Component<IProps, IState> {
         );
     };
 
-    public render() {
+    public render(): JSX.Element {
         const avatarSize = 32; // should match border-radius of the avatar
 
         const userId = MatrixClientPeg.get().getUserId();

src/components/structures/auth/CompleteSecurity.tsx

@@ -57,7 +57,7 @@ export default class CompleteSecurity extends React.Component<IProps, IState> {
         store.stop();
     }
 
-    public render() {
+    public render(): JSX.Element {
         const { phase, lostKeys } = this.state;
         let icon;
         let title;

src/components/structures/auth/E2eSetup.tsx

@@ -27,7 +27,7 @@ interface IProps {
 }
 
 export default class E2eSetup extends React.Component<IProps> {
-    public render() {
+    public render(): JSX.Element {
         return (
             <AuthPage>
                 <CompleteSecurityBody>

src/components/structures/auth/ForgotPassword.tsx

@@ -110,11 +110,11 @@ export default class ForgotPassword extends React.Component<Props, State> {
         this.reset = new PasswordReset(this.props.serverConfig.hsUrl, this.props.serverConfig.isUrl);
     }
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         this.checkServerCapabilities(this.props.serverConfig);
     }
 
-    public componentDidUpdate(prevProps: Readonly<Props>) {
+    public componentDidUpdate(prevProps: Readonly<Props>): void {
         if (
             prevProps.serverConfig.hsUrl !== this.props.serverConfig.hsUrl ||
             prevProps.serverConfig.isUrl !== this.props.serverConfig.isUrl
@@ -159,7 +159,7 @@ export default class ForgotPassword extends React.Component<Props, State> {
         });
     }
 
-    private async onPhaseEmailInputSubmit() {
+    private async onPhaseEmailInputSubmit(): Promise<void> {
         this.phase = Phase.SendingEmail;
 
         if (await this.sendVerificationMail()) {
@@ -213,7 +213,7 @@ export default class ForgotPassword extends React.Component<Props, State> {
         });
     }
 
-    private async onPhaseEmailSentSubmit() {
+    private async onPhaseEmailSentSubmit(): Promise<void> {
         this.setState({
             phase: Phase.PasswordInput,
         });
@@ -288,7 +288,7 @@ export default class ForgotPassword extends React.Component<Props, State> {
             false,
             false,
             {
-                onBeforeClose: async (reason?: string) => {
+                onBeforeClose: async (reason?: string): Promise<boolean> => {
                     if (reason === "backgroundClick") {
                         // Modal dismissed by clicking the background.
                         // Go one phase back.
@@ -342,7 +342,7 @@ export default class ForgotPassword extends React.Component<Props, State> {
         }
     };
 
-    private onInputChanged = (stateKey: string, ev: React.FormEvent<HTMLInputElement>) => {
+    private onInputChanged = (stateKey: string, ev: React.FormEvent<HTMLInputElement>): void => {
         let value = ev.currentTarget.value;
         if (stateKey === "email") value = value.trim();
         this.setState({
@@ -460,7 +460,7 @@ export default class ForgotPassword extends React.Component<Props, State> {
         );
     }
 
-    public renderDone() {
+    public renderDone(): JSX.Element {
         return (
             <>
                 <CheckboxIcon className="mx_Icon mx_Icon_32 mx_Icon_accent" />
@@ -484,7 +484,7 @@ export default class ForgotPassword extends React.Component<Props, State> {
         );
     }
 
-    public render() {
+    public render(): JSX.Element {
         let resetPasswordJsx: JSX.Element;
 
         switch (this.state.phase) {