ref: Convert reducers to TS (#12101)

react/features/app/types.ts

@@ -54,7 +54,21 @@ import { IPollsState } from '../polls/reducer';
 import { IPowerMonitorState } from '../power-monitor/reducer';
 import { IPrejoinState } from '../prejoin/reducer';
 import { IReactionsState } from '../reactions/reducer';
+import { IRecentListState } from '../recent-list/reducer';
+import { IRecordingState } from '../recording/reducer';
+import { IRemoteControlState } from '../remote-control/reducer';
+import { IScreenShareState } from '../screen-share/reducer';
+import { IScreenshotCaptureState } from '../screenshot-capture/reducer';
 import { ISharedVideoState } from '../shared-video/reducer';
+import { ISpeakerStatsState } from '../speaker-stats/reducer';
+import { ISubtitlesState } from '../subtitles/reducer';
+import { ITalkWhileMutedState } from '../talk-while-muted/reducer';
+import { IToolboxState } from '../toolbox/reducer';
+import { ITranscribingState } from '../transcribing/reducer';
+import { IVideoLayoutState } from '../video-layout/reducer';
+import { IVideoQualityPersistedState, IVideoQualityState } from '../video-quality/reducer';
+import { IVideoSipGW } from '../videosipgw/reducer';
+import { IVirtualBackground } from '../virtual-background/reducer';
 
 export interface IStore {
     dispatch: Function,
@@ -120,6 +134,22 @@ export interface IState {
     'features/power-monitor': IPowerMonitorState,
     'features/prejoin': IPrejoinState,
     'features/reactions': IReactionsState,
+    'features/recent-list': IRecentListState,
+    'features/recording': IRecordingState,
+    'features/remote-control': IRemoteControlState,
+    'features/screen-share': IScreenShareState,
+    'features/screenshot-capture': IScreenshotCaptureState,
+    'features/settings': ISettingsState,
     'features/shared-video': ISharedVideoState,
-    'features/testing': ITestingState
+    'features/speaker-stats': ISpeakerStatsState,
+    'features/subtitles': ISubtitlesState,
+    'features/talk-while-muted': ITalkWhileMutedState,
+    'features/testing': ITestingState,
+    'features/toolbox': IToolboxState,
+    'features/transcribing': ITranscribingState,
+    'features/video-layout': IVideoLayoutState,
+    'features/video-quality': IVideoQualityState,
+    'features/video-quality-persistent-storage': IVideoQualityPersistedState,
+    'features/videosipgw': IVideoSipGW,
+    'features/virtual-background': IVirtualBackground
 }

react/features/base/connection/utils.ts

@@ -1,5 +1,3 @@
-/* @flow */
-
 /**
  * Gets a {@link URL} without hash and query/search params from a specific
  * {@code URL}.

react/features/recent-list/reducer.ts

@@ -1,19 +1,30 @@
-import { getURLWithoutParamsNormalized } from '../base/connection';
-import { PersistenceRegistry, ReducerRegistry } from '../base/redux';
+/* eslint-disable lines-around-comment */
+import { getURLWithoutParamsNormalized } from '../base/connection/utils';
+import PersistenceRegistry from '../base/redux/PersistenceRegistry';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import {
     _STORE_CURRENT_CONFERENCE,
     _UPDATE_CONFERENCE_DURATION,
     DELETE_RECENT_LIST_ENTRY
 } from './actionTypes';
+// @ts-ignore
 import { isRecentListEnabled } from './functions';
 
+interface IRecent {
+    conference: string;
+    date: number;
+    duration: number;
+}
+
+export type IRecentListState = IRecent[];
+
 /**
  * The default/initial redux state of the feature {@code recent-list}.
  *
- * @type {Array<Object>}
+ * @type {IRecentListState}
  */
-const DEFAULT_STATE = [];
+const DEFAULT_STATE: IRecentListState = [];
 
 /**
  * The max size of the list.
@@ -35,7 +46,7 @@ PersistenceRegistry.register(STORE_NAME);
 /**
  * Reduces redux actions for the purposes of the feature {@code recent-list}.
  */
-ReducerRegistry.register(STORE_NAME, (state = DEFAULT_STATE, action) => {
+ReducerRegistry.register(STORE_NAME, (state: IRecentListState = DEFAULT_STATE, action) => {
     if (isRecentListEnabled()) {
         switch (action.type) {
         case DELETE_RECENT_LIST_ENTRY:
@@ -55,12 +66,12 @@ ReducerRegistry.register(STORE_NAME, (state = DEFAULT_STATE, action) => {
 /**
  * Deletes a recent list entry based on the url and date of the item.
  *
- * @param {Array<Object>} state - The Redux state.
+ * @param {IRecentListState} state - The Redux state.
  * @param {Object} entryId - The ID object of the entry.
- * @returns {Array<Object>}
+ * @returns {IRecentListState}
  */
 function _deleteRecentListEntry(
-        state: Array<Object>, entryId: Object): Array<Object> {
+        state: Array<IRecent>, entryId: { date: number; url: string; }): Array<IRecent> {
     return state.filter(entry =>
         entry.conference !== entryId.url || entry.date !== entryId.date);
 }
@@ -68,11 +79,11 @@ function _deleteRecentListEntry(
 /**
  * Adds a new list entry to the redux store.
  *
- * @param {Object} state - The redux state of the feature {@code recent-list}.
+ * @param {IRecentListState} state - The redux state of the feature {@code recent-list}.
  * @param {Object} action - The redux action.
  * @returns {Object}
  */
-function _storeCurrentConference(state, { locationURL }) {
+function _storeCurrentConference(state: IRecentListState, { locationURL }: { locationURL: { href: string } }) {
     const conference = locationURL.href;
 
     // If the current conference is already in the list, we remove it to re-add
@@ -96,11 +107,11 @@ function _storeCurrentConference(state, { locationURL }) {
 /**
  * Updates the conference length when left.
  *
- * @param {Object} state - The redux state of the feature {@code recent-list}.
+ * @param {IRecentListState} state - The redux state of the feature {@code recent-list}.
  * @param {Object} action - The redux action.
  * @returns {Object} The next redux state of the feature {@code recent-list}.
  */
-function _updateConferenceDuration(state, { locationURL }) {
+function _updateConferenceDuration(state: IRecentListState, { locationURL }: { locationURL: { href: string } }) {
     if (locationURL && locationURL.href && state.length) {
         const mostRecentIndex = state.length - 1;
         const mostRecent = state[mostRecentIndex];

react/features/recording/reducer.ts

@@ -1,4 +1,4 @@
-import { ReducerRegistry } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import {
     CLEAR_RECORDING_SESSIONS,
@@ -16,6 +16,27 @@ const DEFAULT_STATE = {
     sessionDatas: []
 };
 
+interface SessionData {
+    error?: Error;
+    id?: string;
+    initiator?: Object;
+    liveStreamViewURL?: string;
+    mode?: string;
+    status?: string;
+    terminator?: Object;
+    timestamp?: number;
+}
+
+export interface IRecordingState {
+    disableHighlightMeetingMoment: boolean;
+    pendingNotificationUids: {
+        [key: string]: number|undefined;
+    };
+    selectedRecordingService: string;
+    sessionDatas: Array<SessionData>;
+    streamKey?: string;
+}
+
 /**
  * The name of the Redux store this feature stores its state in.
  */
@@ -25,7 +46,7 @@ const STORE_NAME = 'features/recording';
  * Reduces the Redux actions of the feature features/recording.
  */
 ReducerRegistry.register(STORE_NAME,
-    (state = DEFAULT_STATE, action) => {
+    (state: IRecordingState = DEFAULT_STATE, action) => {
         switch (action.type) {
 
         case CLEAR_RECORDING_SESSIONS:
@@ -86,7 +107,7 @@ ReducerRegistry.register(STORE_NAME,
  * @private
  * @returns {Array} The session datas with the updated session data added.
  */
-function _updateSessionDatas(sessionDatas, newSessionData) {
+function _updateSessionDatas(sessionDatas: SessionData[], newSessionData: SessionData) {
     const hasExistingSessionData = sessionDatas.find(
         sessionData => sessionData.id === newSessionData.id);
     let newSessionDatas;

react/features/remote-control/reducer.ts

@@ -1,4 +1,5 @@
-import { ReducerRegistry, set } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
+import { set } from '../base/redux/functions';
 
 import {
     CAPTURE_EVENTS,
@@ -23,11 +24,25 @@ const DEFAULT_STATE = {
     }
 };
 
+export interface IRemoteControlState {
+    active: boolean;
+    controller: {
+        controlled?: string;
+        isCapturingEvents: boolean;
+        requestedParticipant?: string;
+    };
+    receiver: {
+        controller?: string;
+        enabled: boolean;
+        transport?: Object;
+    }
+}
+
 /**
  * Listen for actions that mutate the remote control state.
  */
 ReducerRegistry.register(
-    'features/remote-control', (state = DEFAULT_STATE, action) => {
+    'features/remote-control', (state: IRemoteControlState = DEFAULT_STATE, action) => {
         switch (action.type) {
         case CAPTURE_EVENTS:
             return {

react/features/screen-share/reducer.ts

@@ -1,5 +1,5 @@
 
-import { ReducerRegistry } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import {
     SET_SCREEN_AUDIO_SHARE_STATE,
@@ -7,10 +7,16 @@ import {
     SET_SCREENSHARE_TRACKS
 } from './actionTypes';
 
+export interface IScreenShareState {
+    captureFrameRate?: number;
+    desktopAudioTrack?: Object;
+    isSharingAudio?: boolean;
+}
+
 /**
  * Reduces the Redux actions of the feature features/screen-share.
  */
-ReducerRegistry.register('features/screen-share', (state = {}, action) => {
+ReducerRegistry.register('features/screen-share', (state: IScreenShareState = {}, action) => {
     const { captureFrameRate, isSharingAudio, desktopAudioTrack } = action;
 
     switch (action.type) {

react/features/screenshot-capture/reducer.ts

@@ -1,6 +1,5 @@
-// @flow
-
-import { PersistenceRegistry, ReducerRegistry } from '../base/redux';
+import PersistenceRegistry from '../base/redux/PersistenceRegistry';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import { SET_SCREENSHOT_CAPTURE } from './actionTypes';
 
@@ -12,7 +11,11 @@ const DEFAULT_STATE = {
     capturesEnabled: false
 };
 
-ReducerRegistry.register('features/screenshot-capture', (state = DEFAULT_STATE, action) => {
+export interface IScreenshotCaptureState {
+    capturesEnabled: boolean;
+}
+
+ReducerRegistry.register('features/screenshot-capture', (state: IScreenshotCaptureState = DEFAULT_STATE, action) => {
     switch (action.type) {
     case SET_SCREENSHOT_CAPTURE: {
         return {

react/features/settings/reducer.ts

@@ -1,13 +1,16 @@
-// @flow
-
-import { ReducerRegistry } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import {
     SET_AUDIO_SETTINGS_VISIBILITY,
     SET_VIDEO_SETTINGS_VISIBILITY
 } from './actionTypes';
 
-ReducerRegistry.register('features/settings', (state = {}, action) => {
+export interface ISettingsState {
+    audioSettingsVisible?: boolean;
+    videoSettingsVisible?: boolean;
+}
+
+ReducerRegistry.register('features/settings', (state: ISettingsState = {}, action) => {
     switch (action.type) {
     case SET_AUDIO_SETTINGS_VISIBILITY:
         return {

react/features/speaker-stats/reducer.ts

@@ -1,8 +1,6 @@
-// @flow
-
 import _ from 'lodash';
 
-import { ReducerRegistry } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import {
     INIT_SEARCH,
@@ -25,7 +23,15 @@ const INITIAL_STATE = {
     showFaceExpressions: false
 };
 
-ReducerRegistry.register('features/speaker-stats', (state = _getInitialState(), action) => {
+export interface ISpeakerStatsState {
+    criteria: string|null;
+    isOpen: boolean;
+    pendingReorder: boolean;
+    showFaceExpressions: boolean;
+    stats: Object;
+}
+
+ReducerRegistry.register('features/speaker-stats', (state: ISpeakerStatsState = INITIAL_STATE, action) => {
     switch (action.type) {
     case INIT_SEARCH:
         return _updateCriteria(state, action);
@@ -46,15 +52,6 @@ ReducerRegistry.register('features/speaker-stats', (state = _getInitialState(),
     return state;
 });
 
-/**
- * Gets the initial state of the feature speaker-stats.
- *
- * @returns {Object}
- */
-function _getInitialState() {
-    return INITIAL_STATE;
-}
-
 /**
  * Reduces a specific Redux action INIT_SEARCH of the feature
  * speaker-stats.
@@ -64,7 +61,7 @@ function _getInitialState() {
  * @private
  * @returns {Object} The new state after the reduction of the specified action.
  */
-function _updateCriteria(state, { criteria }) {
+function _updateCriteria(state: ISpeakerStatsState, { criteria }: { criteria: string|null }) {
     return _.assign(
         {},
         state,
@@ -86,7 +83,7 @@ function _updateCriteria(state, { criteria }) {
  * @private
  * @returns {Object} - The new state after the reduction of the specified action.
  */
-function _updateStats(state, { stats }) {
+function _updateStats(state: ISpeakerStatsState, { stats }: { stats: any }) {
     const finalStats = state.pendingReorder ? stats : state.stats;
 
     if (!state.pendingReorder) {
@@ -122,7 +119,7 @@ function _updateStats(state, { stats }) {
  * @private
  * @returns {Object} The new state after the reduction of the specified action.
  */
-function _initReorderStats(state) {
+function _initReorderStats(state: ISpeakerStatsState) {
     return _.assign(
         {},
         state,

react/features/subtitles/reducer.ts

@@ -1,4 +1,4 @@
-import { ReducerRegistry } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import {
     REMOVE_TRANSCRIPT_MESSAGE,
@@ -14,12 +14,18 @@ const defaultState = {
     _language: 'transcribing.subtitlesOff'
 };
 
+export interface ISubtitlesState {
+    _language: string;
+    _requestingSubtitles: boolean;
+    _transcriptMessages: Map<string, Object>;
+}
+
 /**
  * Listen for actions for the transcription feature to be used by the actions
  * to update the rendered transcription subtitles.
  */
 ReducerRegistry.register('features/subtitles', (
-        state = defaultState, action) => {
+        state: ISubtitlesState = defaultState, action) => {
     switch (action.type) {
     case REMOVE_TRANSCRIPT_MESSAGE:
         return _removeTranscriptMessage(state, action);
@@ -49,7 +55,7 @@ ReducerRegistry.register('features/subtitles', (
  * @returns {Object} The new state of the feature transcription after the
  * reduction of the specified action.
  */
-function _removeTranscriptMessage(state, { transcriptMessageID }) {
+function _removeTranscriptMessage(state: ISubtitlesState, { transcriptMessageID }: { transcriptMessageID: string }) {
     const newTranscriptMessages = new Map(state._transcriptMessages);
 
     // Deletes the key from Map once a final message arrives.
@@ -70,8 +76,8 @@ function _removeTranscriptMessage(state, { transcriptMessageID }) {
  * @returns {Object} The new state of the feature transcription after the
  * reduction of the specified action.
  */
-function _updateTranscriptMessage(state,
-        { transcriptMessageID, newTranscriptMessage }) {
+function _updateTranscriptMessage(state: ISubtitlesState, { transcriptMessageID, newTranscriptMessage }:
+    { newTranscriptMessage: Object, transcriptMessageID: string }) {
     const newTranscriptMessages = new Map(state._transcriptMessages);
 
     // Updates the new message for the given key in the Map.

react/features/talk-while-muted/reducer.ts

@@ -1,13 +1,16 @@
-// @flow
-
-import { ReducerRegistry, set } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
+import { set } from '../base/redux/functions';
 
 import { SET_CURRENT_NOTIFICATION_UID } from './actionTypes';
 
+export interface ITalkWhileMutedState {
+    currentNotificationUid?: number;
+}
+
 /**
  * Reduces the redux actions of the feature talk while muted.
  */
-ReducerRegistry.register('features/talk-while-muted', (state = { }, action) => {
+ReducerRegistry.register('features/talk-while-muted', (state: ITalkWhileMutedState = { }, action) => {
     switch (action.type) {
     case SET_CURRENT_NOTIFICATION_UID:
         return set(state, 'currentNotificationUid', action.uid);

react/features/toolbox/reducer.ts

@@ -1,6 +1,5 @@
-// @flow
-
-import { ReducerRegistry, set } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
+import { set } from '../base/redux/functions';
 
 import {
     CLEAR_TOOLBOX_TIMEOUT,
@@ -73,9 +72,20 @@ const INITIAL_STATE = {
     visible: false
 };
 
+export interface IToolboxState {
+    enabled: boolean;
+    fullScreen?: boolean;
+    hangupMenuVisible: boolean;
+    hovered: boolean;
+    overflowDrawer: boolean;
+    overflowMenuVisible: boolean;
+    timeoutID?: number|null;
+    visible: boolean;
+}
+
 ReducerRegistry.register(
     'features/toolbox',
-    (state: Object = INITIAL_STATE, action: Object) => {
+    (state: IToolboxState = INITIAL_STATE, action): IToolboxState => {
         switch (action.type) {
         case CLEAR_TOOLBOX_TIMEOUT:
             return {

react/features/transcribing/reducer.ts

@@ -1,5 +1,4 @@
-
-import { ReducerRegistry } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import {
     _TRANSCRIBER_JOINED,
@@ -59,11 +58,20 @@ function _getInitialState() {
     };
 }
 
+export interface ITranscribingState {
+    isDialing: boolean;
+    isTerminating: boolean;
+    isTranscribing: boolean;
+    pendingNotificationUid?: number;
+    potentialTranscriberJIDs: string[];
+    transcriberJID?: string|null;
+}
+
 /**
  * Reduces the Redux actions of the feature features/transcribing.
  */
 ReducerRegistry.register('features/transcribing',
-    (state = _getInitialState(), action) => {
+    (state: ITranscribingState = _getInitialState(), action): ITranscribingState => {
         switch (action.type) {
         case _TRANSCRIBER_JOINED:
             return {

react/features/video-layout/reducer.ts

@@ -1,6 +1,4 @@
-// @flow
-
-import { ReducerRegistry } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import {
     SCREEN_SHARE_REMOTE_PARTICIPANTS_UPDATED,
@@ -33,9 +31,15 @@ const DEFAULT_STATE = {
     tileViewEnabled: undefined
 };
 
+export interface IVideoLayoutState {
+    carMode: boolean;
+    remoteScreenShares: string[];
+    tileViewEnabled?: boolean;
+}
+
 const STORE_NAME = 'features/video-layout';
 
-ReducerRegistry.register(STORE_NAME, (state = DEFAULT_STATE, action) => {
+ReducerRegistry.register(STORE_NAME, (state: IVideoLayoutState = DEFAULT_STATE, action): IVideoLayoutState => {
     switch (action.type) {
     case SCREEN_SHARE_REMOTE_PARTICIPANTS_UPDATED:
     case VIRTUAL_SCREENSHARE_REMOTE_PARTICIPANTS_UPDATED:

react/features/video-quality/logger.ts

@@ -1,5 +1,3 @@
-// @flow
-
 import { getLogger } from '../base/logging/functions';
 
 export default getLogger('features/video-quality');

react/features/video-quality/reducer.ts

@@ -1,8 +1,13 @@
-import { SET_CONFIG } from '../base/config';
-import { PersistenceRegistry, ReducerRegistry, set } from '../base/redux';
+import { SET_CONFIG } from '../base/config/actionTypes';
+import { IConfig } from '../base/config/configType';
+import PersistenceRegistry from '../base/redux/PersistenceRegistry';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
+import { set } from '../base/redux/functions';
 
 import { SET_MAX_RECEIVER_VIDEO_QUALITY, SET_PREFERRED_VIDEO_QUALITY } from './actionTypes';
 import { VIDEO_QUALITY_LEVELS } from './constants';
+/* eslint-disable-next-line lines-around-comment */
+// @ts-ignore
 import { validateMinHeightForQualityLvl } from './functions';
 import logger from './logger';
 
@@ -15,12 +20,23 @@ const DEFAULT_STATE = {
 DEFAULT_STATE.minHeightForQualityLvl.set(360, VIDEO_QUALITY_LEVELS.STANDARD);
 DEFAULT_STATE.minHeightForQualityLvl.set(720, VIDEO_QUALITY_LEVELS.HIGH);
 
+export interface IVideoQualityState {
+    maxReceiverVideoQuality: number;
+    minHeightForQualityLvl: Map<number, number>;
+    preferredVideoQuality: number;
+}
+
+export interface IVideoQualityPersistedState {
+    persistedPrefferedVideoQuality?: number;
+}
+
 
 // When the persisted state is initialized the current state (for example the default state) is erased.
 // In order to workaround this issue we need additional state for the persisted properties.
 PersistenceRegistry.register('features/video-quality-persistent-storage');
 
-ReducerRegistry.register('features/video-quality-persistent-storage', (state = {}, action) => {
+ReducerRegistry.register('features/video-quality-persistent-storage',
+(state: IVideoQualityPersistedState = {}, action): IVideoQualityPersistedState => {
     switch (action.type) {
     case SET_PREFERRED_VIDEO_QUALITY: {
         const { preferredVideoQuality } = action;
@@ -35,7 +51,8 @@ ReducerRegistry.register('features/video-quality-persistent-storage', (state = {
     return state;
 });
 
-ReducerRegistry.register('features/video-quality', (state = DEFAULT_STATE, action) => {
+ReducerRegistry.register('features/video-quality',
+(state: IVideoQualityState = DEFAULT_STATE, action): IVideoQualityState => {
     switch (action.type) {
     case SET_CONFIG:
         return _setConfig(state, action);
@@ -65,7 +82,7 @@ ReducerRegistry.register('features/video-quality', (state = DEFAULT_STATE, actio
  * @private
  * @returns {Object} The new state after the reduction of the specified action.
  */
-function _setConfig(state, { config }) {
+function _setConfig(state: IVideoQualityState, { config }: { config: IConfig }) {
     const configuredMap = config?.videoQuality?.minHeightForQualityLvl;
     const convertedMap = validateMinHeightForQualityLvl(configuredMap);
 

react/features/videosipgw/reducer.ts

@@ -1,9 +1,13 @@
-import { ReducerRegistry } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import { SIP_GW_AVAILABILITY_CHANGED } from './actionTypes';
 
+export interface IVideoSipGW {
+    status?: string;
+}
+
 ReducerRegistry.register(
-    'features/videosipgw', (state = [], action) => {
+    'features/videosipgw', (state: IVideoSipGW = {}, action): IVideoSipGW => {
         switch (action.type) {
         case SIP_GW_AVAILABILITY_CHANGED: {
             return {

react/features/virtual-background/reducer.ts

@@ -1,12 +1,19 @@
-// @flow
-
-import { PersistenceRegistry, ReducerRegistry } from '../base/redux';
+import PersistenceRegistry from '../base/redux/PersistenceRegistry';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import { BACKGROUND_ENABLED, SET_VIRTUAL_BACKGROUND } from './actionTypes';
 import { VIRTUAL_BACKGROUND_TYPE } from './constants';
 
 const STORE_NAME = 'features/virtual-background';
 
+export interface IVirtualBackground {
+    backgroundEffectEnabled?: boolean;
+    backgroundType?: string;
+    blurValue?: number;
+    selectedThumbnail?: string;
+    virtualSource?: string;
+}
+
 /**
  * Reduces redux actions which activate/deactivate virtual background image, or
  * indicate if the virtual image background is activated/deactivated. The
@@ -18,7 +25,7 @@ const STORE_NAME = 'features/virtual-background';
  * @returns {State} The next redux state that is the result of reducing the
  * specified action.
  */
-ReducerRegistry.register(STORE_NAME, (state = {}, action) => {
+ReducerRegistry.register(STORE_NAME, (state: IVirtualBackground = {}, action): IVirtualBackground => {
     const { virtualSource, backgroundEffectEnabled, blurValue, backgroundType, selectedThumbnail } = action;
 
     /**