diff --git a/react/features/app/types.ts b/react/features/app/types.ts
index eca11d08e..8ff940e5d 100644
--- a/react/features/app/types.ts
+++ b/react/features/app/types.ts
@@ -36,6 +36,10 @@ import { IFilmstripState } from '../filmstrip/reducer';
 import { IFollowMeState } from '../follow-me/reducer';
 import { IGifsState } from '../gifs/reducer';
 import { IGoogleApiState } from '../google-api/reducer';
+import { IInviteState } from '../invite/reducer';
+import { IJaaSState } from '../jaas/reducer';
+import { ILargeVideoState } from '../large-video/reducer';
+import { ILobbyState } from '../lobby/reducer';
 import { INoiseSuppressionState } from '../noise-suppression/reducer';
 
 export interface IStore {
@@ -83,6 +87,10 @@ export interface IState {
     'features/follow-me': IFollowMeState,
     'features/gifs': IGifsState,
     'features/google-api': IGoogleApiState,
+    'features/invite': IInviteState,
+    'features/jaas': IJaaSState,
+    'features/large-video': ILargeVideoState,
+    'features/lobby': ILobbyState,
     'features/noise-suppression': INoiseSuppressionState,
     'features/testing': ITestingState
 }
diff --git a/react/features/invite/logger.js b/react/features/invite/logger.ts
similarity index 90%
rename from react/features/invite/logger.js
rename to react/features/invite/logger.ts
index 4e9e3106f..d57552b8e 100644
--- a/react/features/invite/logger.js
+++ b/react/features/invite/logger.ts
@@ -1,5 +1,3 @@
-// @flow
-
 import { getLogger } from '../base/logging/functions';
 
 export default getLogger('features/invite');
diff --git a/react/features/invite/reducer.js b/react/features/invite/reducer.ts
similarity index 79%
rename from react/features/invite/reducer.js
rename to react/features/invite/reducer.ts
index 73be613bb..2efc4080e 100644
--- a/react/features/invite/reducer.js
+++ b/react/features/invite/reducer.ts
@@ -1,6 +1,4 @@
-// @flow
-
-import { ReducerRegistry } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import {
     ADD_PENDING_INVITE_REQUEST,
@@ -24,7 +22,22 @@ const DEFAULT_STATE = {
     pendingInviteRequests: []
 };
 
-ReducerRegistry.register('features/invite', (state = DEFAULT_STATE, action) => {
+export interface IInviteState {
+    calleeInfoVisible?: boolean;
+    conferenceID?: string;
+    error?: Error;
+    initialCalleeInfo?: Object;
+    numbers?: string;
+    numbersEnabled: boolean;
+    numbersFetched: boolean;
+    pendingInviteRequests: Array<{
+        callback: Function;
+        invitees: Array<Object>;
+    }>;
+    sipUri?: string;
+}
+
+ReducerRegistry.register('features/invite', (state: IInviteState = DEFAULT_STATE, action) => {
     switch (action.type) {
     case ADD_PENDING_INVITE_REQUEST:
         return {
diff --git a/react/features/jaas/constants.js b/react/features/jaas/constants.ts
similarity index 100%
rename from react/features/jaas/constants.js
rename to react/features/jaas/constants.ts
diff --git a/react/features/jaas/reducer.js b/react/features/jaas/reducer.ts
similarity index 69%
rename from react/features/jaas/reducer.js
rename to react/features/jaas/reducer.ts
index b15cdd356..af82206b8 100644
--- a/react/features/jaas/reducer.js
+++ b/react/features/jaas/reducer.ts
@@ -1,4 +1,4 @@
-import { ReducerRegistry } from '../base/redux';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import {
     SET_DETAILS
@@ -10,11 +10,15 @@ const DEFAULT_STATE = {
     status: STATUSES.ACTIVE
 };
 
+export interface IJaaSState {
+    [key: string]: any
+}
+
 /**
  * Listen for actions that mutate the billing-counter state.
  */
 ReducerRegistry.register(
-    'features/jaas', (state = DEFAULT_STATE, action) => {
+    'features/jaas', (state: IJaaSState = DEFAULT_STATE, action) => {
         switch (action.type) {
 
         case SET_DETAILS: {
diff --git a/react/features/large-video/reducer.js b/react/features/large-video/reducer.ts
similarity index 78%
rename from react/features/large-video/reducer.js
rename to react/features/large-video/reducer.ts
index 5266c97b2..a1f542f17 100644
--- a/react/features/large-video/reducer.js
+++ b/react/features/large-video/reducer.ts
@@ -1,7 +1,5 @@
-// @flow
-
-import { PARTICIPANT_ID_CHANGED } from '../base/participants';
-import { ReducerRegistry } from '../base/redux';
+import { PARTICIPANT_ID_CHANGED } from '../base/participants/actionTypes';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import {
     SELECT_LARGE_VIDEO_PARTICIPANT,
@@ -10,7 +8,14 @@ import {
     SET_SEE_WHAT_IS_BEING_SHARED
 } from './actionTypes';
 
-ReducerRegistry.register('features/large-video', (state = {}, action) => {
+export interface ILargeVideoState {
+    lastMediaEvent?: string;
+    participantId?: string;
+    resolution?: number;
+    seeWhatIsBeingShared?: boolean;
+}
+
+ReducerRegistry.register('features/large-video', (state: ILargeVideoState = {}, action) => {
     switch (action.type) {
 
     // When conference is joined, we update ID of local participant from default
diff --git a/react/features/lobby/reducer.js b/react/features/lobby/reducer.ts
similarity index 85%
rename from react/features/lobby/reducer.js
rename to react/features/lobby/reducer.ts
index 5f9c3d62f..ac4fad521 100644
--- a/react/features/lobby/reducer.js
+++ b/react/features/lobby/reducer.ts
@@ -1,7 +1,7 @@
-// @flow
-
+// @ts-ignore
 import { CONFERENCE_JOINED, CONFERENCE_LEFT, SET_PASSWORD } from '../base/conference';
-import { ReducerRegistry } from '../base/redux';
+import { Participant } from '../base/participants/reducer';
+import ReducerRegistry from '../base/redux/ReducerRegistry';
 
 import {
     KNOCKING_PARTICIPANT_ARRIVED_OR_UPDATED,
@@ -22,6 +22,18 @@ const DEFAULT_STATE = {
     passwordJoinFailed: false
 };
 
+interface KnockingParticipant extends Participant {
+    chattingWithModerator?: string;
+}
+
+export interface ILobbyState {
+    knocking: boolean;
+    knockingParticipants: KnockingParticipant[];
+    lobbyEnabled: boolean;
+    lobbyVisible: boolean;
+    passwordJoinFailed: boolean;
+}
+
 /**
  * Reduces redux actions which affect the display of notifications.
  *
@@ -30,7 +42,7 @@ const DEFAULT_STATE = {
  * @returns {Object} The next redux state which is the result of reducing the
  * specified {@code action}.
  */
-ReducerRegistry.register('features/lobby', (state = DEFAULT_STATE, action) => {
+ReducerRegistry.register('features/lobby', (state: ILobbyState = DEFAULT_STATE, action) => {
     switch (action.type) {
     case CONFERENCE_JOINED:
     case CONFERENCE_LEFT:
@@ -112,7 +124,7 @@ ReducerRegistry.register('features/lobby', (state = DEFAULT_STATE, action) => {
  * @param {Object} state - The current Redux state of the feature.
  * @returns {Object}
  */
-function _knockingParticipantArrivedOrUpdated(participant, state) {
+function _knockingParticipantArrivedOrUpdated(participant: KnockingParticipant, state: ILobbyState) {
     let existingParticipant = state.knockingParticipants.find(p => p.id === participant.id);
 
     existingParticipant = {