diff --git a/react/features/app/types.ts b/react/features/app/types.ts
index 6e3527987..f8af433fc 100644
--- a/react/features/app/types.ts
+++ b/react/features/app/types.ts
@@ -22,6 +22,14 @@ import { ISoundsState } from '../base/sounds/reducer';
 import { ITestingState } from '../base/testing/reducer';
 import { INoSrcDataState, ITracksState } from '../base/tracks/reducer';
 import { IUserInteractionState } from '../base/user-interaction/reducer';
+import { IBreakoutRoomsState } from '../breakout-rooms/reducer';
+import { ICalendarSyncState } from '../calendar-sync/reducer';
+import { IChatState } from '../chat/reducer';
+import { IDeepLinkingState } from '../deep-linking/reducer';
+import { IDropboxState } from '../dropbox/reducer';
+import { IDynamicBrandingState } from '../dynamic-branding/reducer';
+import { IE2EEState } from '../e2ee/reducer';
+import { IEtherpadState } from '../etherpad/reducer';
 import { INoiseSuppressionState } from '../noise-suppression/reducer';
 
 export interface IStore {
@@ -55,6 +63,14 @@ export interface IState {
     'features/base/sounds': ISoundsState,
     'features/base/tracks': ITracksState,
     'features/base/user-interaction': IUserInteractionState,
+    'features/breakout-rooms': IBreakoutRoomsState,
+    'features/calendar-sync': ICalendarSyncState,
+    'features/chat': IChatState,
+    'features/deep-linking': IDeepLinkingState,
+    'features/dropbox': IDropboxState,
+    'features/dynamic-branding': IDynamicBrandingState,
+    'features/e2ee': IE2EEState,
+    'features/etherpad': IEtherpadState,
     'features/noise-suppression': INoiseSuppressionState,
     'features/testing': ITestingState
 }
diff --git a/react/features/base/participants/reducer.ts b/react/features/base/participants/reducer.ts
index de311daa1..8ae007bf6 100644
--- a/react/features/base/participants/reducer.ts
+++ b/react/features/base/participants/reducer.ts
@@ -67,7 +67,7 @@ export interface Participant {
     supportsRemoteControl?: boolean;
 }
 
-interface LocalParticipant extends Participant {
+export interface LocalParticipant extends Participant {
     audioOutputDeviceId?: string;
     cameraDeviceId?: string;
     micDeviceId?: string;
diff --git a/react/features/breakout-rooms/constants.js b/react/features/breakout-rooms/constants.ts
similarity index 100%
rename from react/features/breakout-rooms/constants.js
rename to react/features/breakout-rooms/constants.ts
diff --git a/react/features/breakout-rooms/reducer.js b/react/features/breakout-rooms/reducer.ts
similarity index 54%
rename from react/features/breakout-rooms/reducer.js
rename to react/features/breakout-rooms/reducer.ts
index abc2aeb20..f08cab01c 100644
--- a/react/features/breakout-rooms/reducer.js
+++ b/react/features/breakout-rooms/reducer.ts
@@ -1,6 +1,4 @@
-// @flow
-
-import { ReducerRegistry } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import {
     _RESET_BREAKOUT_ROOMS,
@@ -14,10 +12,29 @@ const DEFAULT_STATE = {
     roomCounter: 0
 };
 
+export interface IBreakoutRoomsState {
+    roomCounter: number;
+    rooms: {
+        [id: string]: {
+            id: string;
+            isMainRoom?: boolean;
+            jid: string;
+            name: string;
+            participants: {
+                [jid: string]: {
+                    displayName: string;
+                    jid: string;
+                    role: string;
+                }
+            }
+        }
+    };
+}
+
 /**
  * Listen for actions for the breakout-rooms feature.
  */
-ReducerRegistry.register(FEATURE_KEY, (state = DEFAULT_STATE, action) => {
+ReducerRegistry.register(FEATURE_KEY, (state: IBreakoutRoomsState = DEFAULT_STATE, action: any) => {
     switch (action.type) {
     case _UPDATE_ROOM_COUNTER:
         return {
diff --git a/react/features/calendar-sync/reducer.js b/react/features/calendar-sync/reducer.tsx
similarity index 81%
rename from react/features/calendar-sync/reducer.js
rename to react/features/calendar-sync/reducer.tsx
index c243c0ae9..dfbf4b174 100644
--- a/react/features/calendar-sync/reducer.js
+++ b/react/features/calendar-sync/reducer.tsx
@@ -1,6 +1,6 @@
-// @flow
-
-import { PersistenceRegistry, ReducerRegistry, set } from '../base/redux';
+import PersistenceRegistry from '../base/redux/PersistenceRegistry';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
+import { set } from '../base/redux/functions';
 
 import {
     CLEAR_CALENDAR_INTEGRATION,
@@ -26,6 +26,17 @@ const DEFAULT_STATE = {
     msAuthState: undefined
 };
 
+export interface ICalendarSyncState {
+    authorization?: string;
+    error?: Object;
+    events: Array<Object>;
+    integrationReady: boolean;
+    integrationType?: string;
+    isLoadingEvents?: boolean;
+    msAuthState?: Object;
+    profileEmail?: string;
+}
+
 /**
  * Constant for the Redux subtree of the calendar feature.
  *
@@ -47,7 +58,7 @@ PersistenceRegistry.register(STORE_NAME, {
     msAuthState: true
 });
 
-ReducerRegistry.register(STORE_NAME, (state = DEFAULT_STATE, action) => {
+ReducerRegistry.register(STORE_NAME, (state: ICalendarSyncState = DEFAULT_STATE, action) => {
     switch (action.type) {
     case CLEAR_CALENDAR_INTEGRATION:
         return DEFAULT_STATE;
diff --git a/react/features/chat/reducer.js b/react/features/chat/reducer.ts
similarity index 82%
rename from react/features/chat/reducer.js
rename to react/features/chat/reducer.ts
index 54ae0e048..e53514618 100644
--- a/react/features/chat/reducer.js
+++ b/react/features/chat/reducer.ts
@@ -1,8 +1,7 @@
-// @flow
-
 import { v4 as uuidv4 } from 'uuid';
 
-import { ReducerRegistry } from '../base/redux';
+import { LocalParticipant, Participant } from '../base/participants/reducer';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import {
     ADD_MESSAGE,
@@ -21,7 +20,6 @@ const DEFAULT_STATE = {
     isOpen: false,
     isPollsTabFocused: false,
     lastReadMessage: undefined,
-    lastReadPoll: undefined,
     messages: [],
     nbUnreadMessages: 0,
     privateMessageRecipient: undefined,
@@ -29,10 +27,38 @@ const DEFAULT_STATE = {
     isLobbyChatActive: false
 };
 
-ReducerRegistry.register('features/chat', (state = DEFAULT_STATE, action) => {
+interface IMessage {
+    displayName: string;
+    error?: Object;
+    id: string;
+    isReaction: boolean;
+    lobbyChat: boolean;
+    message: string;
+    messageId: string;
+    messageType: string;
+    privateMessage: boolean;
+    recipient: string;
+    timestamp: string;
+}
+
+export interface IChatState {
+    isLobbyChatActive: boolean;
+    isOpen: boolean;
+    isPollsTabFocused: boolean;
+    lastReadMessage?: IMessage;
+    lobbyMessageRecipient?: {
+        id: string;
+        name: string;
+    } | LocalParticipant,
+    messages: IMessage[];
+    nbUnreadMessages: number;
+    privateMessageRecipient?: Participant;
+}
+
+ReducerRegistry.register('features/chat', (state: IChatState = DEFAULT_STATE, action) => {
     switch (action.type) {
     case ADD_MESSAGE: {
-        const newMessage = {
+        const newMessage: IMessage = {
             displayName: action.displayName,
             error: action.error,
             id: action.id,
diff --git a/react/features/deep-linking/reducer.js b/react/features/deep-linking/reducer.ts
similarity index 69%
rename from react/features/deep-linking/reducer.js
rename to react/features/deep-linking/reducer.ts
index 2ef34a041..c44319cf0 100644
--- a/react/features/deep-linking/reducer.js
+++ b/react/features/deep-linking/reducer.ts
@@ -1,9 +1,11 @@
-/* @flow */
-
-import { ReducerRegistry } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import { OPEN_WEB_APP } from './actionTypes';
 
+export interface IDeepLinkingState {
+    launchInWeb?: boolean;
+}
+
 ReducerRegistry.register('features/deep-linking', (state = {}, action) => {
     switch (action.type) {
     case OPEN_WEB_APP: {
diff --git a/react/features/dropbox/reducer.js b/react/features/dropbox/reducer.ts
similarity index 62%
rename from react/features/dropbox/reducer.js
rename to react/features/dropbox/reducer.ts
index 60362e79f..dcc504e3d 100644
--- a/react/features/dropbox/reducer.js
+++ b/react/features/dropbox/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 { UPDATE_DROPBOX_TOKEN } from './actionTypes';
 
@@ -9,12 +8,18 @@ import { UPDATE_DROPBOX_TOKEN } from './actionTypes';
  */
 const STORE_NAME = 'features/dropbox';
 
+export interface IDropboxState {
+    expireDate?: number;
+    rToken?: string;
+    token?: string;
+}
+
 /**
  * Sets up the persistence of the feature {@code dropbox}.
  */
 PersistenceRegistry.register(STORE_NAME);
 
-ReducerRegistry.register(STORE_NAME, (state = {}, action) => {
+ReducerRegistry.register(STORE_NAME, (state: IDropboxState = {}, action) => {
     switch (action.type) {
     case UPDATE_DROPBOX_TOKEN:
         return {
diff --git a/react/features/dynamic-branding/reducer.js b/react/features/dynamic-branding/reducer.ts
similarity index 86%
rename from react/features/dynamic-branding/reducer.js
rename to react/features/dynamic-branding/reducer.ts
index 5f6558e6d..95a04b499 100644
--- a/react/features/dynamic-branding/reducer.js
+++ b/react/features/dynamic-branding/reducer.ts
@@ -1,6 +1,4 @@
-// @flow
-
-import { ReducerRegistry } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 import { type Image } from '../virtual-background/constants';
 
 import {
@@ -144,10 +142,28 @@ const DEFAULT_STATE = {
     virtualBackgrounds: []
 };
 
+export interface IDynamicBrandingState {
+    avatarBackgrounds: string[];
+    backgroundColor: string;
+    backgroundImageUrl: string;
+    customizationFailed: boolean;
+    customizationReady: boolean;
+    defaultBranding: boolean;
+    didPageUrl: string;
+    inviteDomain: string;
+    labels: Object|null;
+    logoClickUrl: string;
+    logoImageUrl: string;
+    muiBrandedTheme?: boolean;
+    premeetingBackground: string;
+    useDynamicBrandingData: boolean;
+    virtualBackgrounds: Array<Image>;
+}
+
 /**
  * Reduces redux actions for the purposes of the feature {@code dynamic-branding}.
  */
-ReducerRegistry.register(STORE_NAME, (state = DEFAULT_STATE, action) => {
+ReducerRegistry.register(STORE_NAME, (state: IDynamicBrandingState = DEFAULT_STATE, action) => {
     switch (action.type) {
     case SET_DYNAMIC_BRANDING_DATA: {
         const {
@@ -212,7 +228,7 @@ ReducerRegistry.register(STORE_NAME, (state = DEFAULT_STATE, action) => {
  * @private
  * @returns {{Props}}
  */
-function formatImages(images: Array<string> | Array<Object>): Array<Image> {
+function formatImages(images: Array<string> | Array<{src: string; tooltip?: string}>): Array<Image> {
     return images.map((img, i) => {
         let src;
         let tooltip;
diff --git a/react/features/e2ee/constants.js b/react/features/e2ee/constants.ts
similarity index 99%
rename from react/features/e2ee/constants.js
rename to react/features/e2ee/constants.ts
index f09cdc268..4e0313def 100644
--- a/react/features/e2ee/constants.js
+++ b/react/features/e2ee/constants.ts
@@ -1,5 +1,3 @@
-// @flow
-
 /**
  * The identifier of the sound to be played when e2ee is disabled.
  *
diff --git a/react/features/e2ee/reducer.js b/react/features/e2ee/reducer.ts
similarity index 75%
rename from react/features/e2ee/reducer.js
rename to react/features/e2ee/reducer.ts
index ed757de90..d31377675 100644
--- a/react/features/e2ee/reducer.js
+++ b/react/features/e2ee/reducer.ts
@@ -1,6 +1,4 @@
-// @flow
-
-import { ReducerRegistry } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import {
     SET_EVERYONE_ENABLED_E2EE,
@@ -15,10 +13,17 @@ const DEFAULT_STATE = {
     maxMode: MAX_MODE.DISABLED
 };
 
+export interface IE2EEState {
+    enabled: boolean;
+    everyoneEnabledE2EE?: boolean;
+    everyoneSupportE2EE?: boolean;
+    maxMode: string;
+}
+
 /**
  * Reduces the Redux actions of the feature features/e2ee.
  */
-ReducerRegistry.register('features/e2ee', (state = DEFAULT_STATE, action) => {
+ReducerRegistry.register('features/e2ee', (state: IE2EEState = DEFAULT_STATE, action) => {
     switch (action.type) {
     case TOGGLE_E2EE:
         return {
diff --git a/react/features/etherpad/reducer.js b/react/features/etherpad/reducer.ts
similarity index 80%
rename from react/features/etherpad/reducer.js
rename to react/features/etherpad/reducer.ts
index e9bacb9c1..12406ee30 100644
--- a/react/features/etherpad/reducer.js
+++ b/react/features/etherpad/reducer.ts
@@ -1,6 +1,4 @@
-// @flow
-
-import { ReducerRegistry } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import { SET_DOCUMENT_EDITING_STATUS, SET_DOCUMENT_URL } from './actionTypes';
 
@@ -20,12 +18,17 @@ const DEFAULT_STATE = {
     editing: false
 };
 
+export interface IEtherpadState {
+    documentUrl?: string;
+    editing: boolean;
+}
+
 /**
  * Reduces the Redux actions of the feature features/etherpad.
  */
 ReducerRegistry.register(
     'features/etherpad',
-    (state = DEFAULT_STATE, action) => {
+    (state: IEtherpadState = DEFAULT_STATE, action) => {
         switch (action.type) {
         case SET_DOCUMENT_EDITING_STATUS:
             return {
diff --git a/react/features/virtual-background/constants.js b/react/features/virtual-background/constants.ts
similarity index 96%
rename from react/features/virtual-background/constants.js
rename to react/features/virtual-background/constants.ts
index bfd7dcaf9..cda33f391 100644
--- a/react/features/virtual-background/constants.js
+++ b/react/features/virtual-background/constants.ts
@@ -1,5 +1,3 @@
-// @flow
-
 /**
  * An enumeration of the different virtual background types.
  *
@@ -14,9 +12,9 @@ export const VIRTUAL_BACKGROUND_TYPE = {
 
 
 export type Image = {
-    tooltip?: string,
     id: string,
-    src: string
+    src: string,
+    tooltip?: string
 }
 
 // The limit of virtual background uploads is 24. When the number