diff --git a/web/account/siwe-login-form.react.js b/web/account/siwe-login-form.react.js
--- a/web/account/siwe-login-form.react.js
+++ b/web/account/siwe-login-form.react.js
@@ -17,7 +17,10 @@
 import SWMansionIcon from 'lib/components/SWMansionIcon.react.js';
 import stores from 'lib/facts/stores.js';
 import { createLoadingStatusSelector } from 'lib/selectors/loading-selectors.js';
-import type { LogInStartingPayload } from 'lib/types/account-types.js';
+import type {
+  LogInStartingPayload,
+  LogInExtraInfo,
+} from 'lib/types/account-types.js';
 import type {
   OLMIdentityKeys,
   SignedIdentityKeysBlob,
@@ -92,7 +95,7 @@
     useSignedIdentityKeysBlob();
 
   const callSIWEAuthEndpoint = React.useCallback(
-    async (message: string, signature: string, extraInfo) => {
+    async (message: string, signature: string, extraInfo: LogInExtraInfo) => {
       invariant(
         signedIdentityKeysBlob,
         'signedIdentityKeysBlob must be set in attemptSIWEAuth',
diff --git a/web/account/traditional-login-form.react.js b/web/account/traditional-login-form.react.js
--- a/web/account/traditional-login-form.react.js
+++ b/web/account/traditional-login-form.react.js
@@ -45,20 +45,26 @@
   }, []);
 
   const [username, setUsername] = React.useState<string>('');
-  const onUsernameChange = React.useCallback(e => {
-    invariant(e.target instanceof HTMLInputElement, 'target not input');
-    setUsername(e.target.value);
-  }, []);
+  const onUsernameChange = React.useCallback(
+    (e: SyntheticEvent<HTMLInputElement>) => {
+      invariant(e.target instanceof HTMLInputElement, 'target not input');
+      setUsername(e.target.value);
+    },
+    [],
+  );
 
   const onUsernameBlur = React.useCallback(() => {
     setUsername(untrimmedUsername => untrimmedUsername.trim());
   }, []);
 
   const [password, setPassword] = React.useState<string>('');
-  const onPasswordChange = React.useCallback(e => {
-    invariant(e.target instanceof HTMLInputElement, 'target not input');
-    setPassword(e.target.value);
-  }, []);
+  const onPasswordChange = React.useCallback(
+    (e: SyntheticEvent<HTMLInputElement>) => {
+      invariant(e.target instanceof HTMLInputElement, 'target not input');
+      setPassword(e.target.value);
+    },
+    [],
+  );
 
   const [errorMessage, setErrorMessage] = React.useState<string>('');
 
diff --git a/web/app.react.js b/web/app.react.js
--- a/web/app.react.js
+++ b/web/app.react.js
@@ -165,7 +165,7 @@
     });
   };
 
-  render() {
+  render(): React.Node {
     let content;
     if (this.props.loggedIn) {
       content = (
@@ -213,10 +213,11 @@
     );
   }
 
-  onHeaderDoubleClick = () => electron?.doubleClickTopBar();
-  stopDoubleClickPropagation = electron ? e => e.stopPropagation() : null;
+  onHeaderDoubleClick = (): void => electron?.doubleClickTopBar();
+  stopDoubleClickPropagation: ?(SyntheticEvent<HTMLAnchorElement>) => void =
+    electron ? e => e.stopPropagation() : null;
 
-  renderLoginPage() {
+  renderLoginPage(): React.Node {
     const { loginMethod } = this.props.navInfo;
 
     if (loginMethod === 'qr-code') {
@@ -226,7 +227,7 @@
     return <Splash />;
   }
 
-  renderMainContent() {
+  renderMainContent(): React.Node {
     const mainContent = this.getMainContentWithSwitcher();
 
     let navigationArrows = null;
@@ -284,7 +285,7 @@
     );
   }
 
-  getMainContentWithSwitcher() {
+  getMainContentWithSwitcher(): React.Node {
     const { tab, settingsSection } = this.props.navInfo;
     let mainContent;
 
diff --git a/web/avatars/edit-thread-avatar-menu.react.js b/web/avatars/edit-thread-avatar-menu.react.js
--- a/web/avatars/edit-thread-avatar-menu.react.js
+++ b/web/avatars/edit-thread-avatar-menu.react.js
@@ -57,8 +57,10 @@
 
   const uploadAvatarMedia = useUploadAvatarMedia();
   const onImageSelected = React.useCallback(
-    async event => {
-      const uploadResult = await uploadAvatarMedia(event.target.files[0]);
+    async (event: SyntheticEvent<HTMLInputElement>) => {
+      const { target } = event;
+      invariant(target instanceof HTMLInputElement, 'target not input');
+      const uploadResult = await uploadAvatarMedia(target.files[0]);
       baseSetThreadAvatar(threadInfo.id, {
         type: 'image',
         uploadID: uploadResult.id,
diff --git a/web/avatars/edit-user-avatar-menu.react.js b/web/avatars/edit-user-avatar-menu.react.js
--- a/web/avatars/edit-user-avatar-menu.react.js
+++ b/web/avatars/edit-user-avatar-menu.react.js
@@ -69,8 +69,10 @@
 
   const uploadAvatarMedia = useUploadAvatarMedia();
   const onImageSelected = React.useCallback(
-    async event => {
-      const uploadResult = await uploadAvatarMedia(event.target.files[0]);
+    async (event: SyntheticEvent<HTMLInputElement>) => {
+      const { target } = event;
+      invariant(target instanceof HTMLInputElement, 'target not input');
+      const uploadResult = await uploadAvatarMedia(target.files[0]);
       baseSetUserAvatar({ type: 'image', uploadID: uploadResult.id });
     },
     [baseSetUserAvatar, uploadAvatarMedia],
diff --git a/web/avatars/emoji-avatar-selection-modal.react.js b/web/avatars/emoji-avatar-selection-modal.react.js
--- a/web/avatars/emoji-avatar-selection-modal.react.js
+++ b/web/avatars/emoji-avatar-selection-modal.react.js
@@ -53,10 +53,13 @@
     [pendingAvatarColor, pendingAvatarEmoji],
   );
 
-  const onEmojiSelect = React.useCallback(selection => {
-    setUpdateAvatarStatus();
-    setPendingAvatarEmoji(selection.native);
-  }, []);
+  const onEmojiSelect = React.useCallback(
+    (selection: { +native: string, ... }) => {
+      setUpdateAvatarStatus();
+      setPendingAvatarEmoji(selection.native);
+    },
+    [],
+  );
 
   const onColorSelection = React.useCallback((hex: string) => {
     setUpdateAvatarStatus();
diff --git a/web/calendar/calendar.react.js b/web/calendar/calendar.react.js
--- a/web/calendar/calendar.react.js
+++ b/web/calendar/calendar.react.js
@@ -41,6 +41,11 @@
 import type { NavInfo } from '../types/nav-types.js';
 import { canonicalURLFromReduxState } from '../url-utils.js';
 
+type StartAndEndDates = {
+  +startDate: string,
+  +endDate: string,
+};
+
 type BaseProps = {
   +url: string,
 };
@@ -69,7 +74,7 @@
     dayOfMonth: number,
     monthInput: ?number = undefined,
     yearInput: ?number = undefined,
-  ) {
+  ): Date {
     return getDate(
       yearInput ? yearInput : this.props.year,
       monthInput ? monthInput : this.props.month,
@@ -77,7 +82,7 @@
     );
   }
 
-  prevMonthDates() {
+  prevMonthDates(): StartAndEndDates {
     const { year, month } = this.props;
     const lastMonthDate = getDate(year, month - 1, 1);
     const prevYear = lastMonthDate.getFullYear();
@@ -88,7 +93,7 @@
     };
   }
 
-  nextMonthDates() {
+  nextMonthDates(): StartAndEndDates {
     const { year, month } = this.props;
     const nextMonthDate = getDate(year, month + 1, 1);
     const nextYear = nextMonthDate.getFullYear();
@@ -99,7 +104,7 @@
     };
   }
 
-  render() {
+  render(): React.Node {
     const { year, month } = this.props;
     const monthName = dateFormat(getDate(year, month, 1), 'mmmm');
     const prevURL = canonicalURLFromReduxState(
diff --git a/web/calendar/day.react.js b/web/calendar/day.react.js
--- a/web/calendar/day.react.js
+++ b/web/calendar/day.react.js
@@ -65,7 +65,7 @@
     }
   }
 
-  render() {
+  render(): React.Node {
     const now = new Date();
     const isToday = dateString(now) === this.props.dayString;
     const tdClasses = classNames(css.day, { [css.currentDay]: isToday });
diff --git a/web/calendar/filter-panel.react.js b/web/calendar/filter-panel.react.js
--- a/web/calendar/filter-panel.react.js
+++ b/web/calendar/filter-panel.react.js
@@ -77,7 +77,7 @@
     return this.props.filteredCommunityThreadIDs.has(threadID);
   }
 
-  render() {
+  render(): React.Node {
     const filterThreadInfos = this.state.query
       ? this.state.searchResults
       : this.props.filterThreadInfos;
@@ -275,7 +275,7 @@
   +selected: boolean,
 };
 class Item extends React.PureComponent<ItemProps> {
-  render() {
+  render(): React.Node {
     const threadInfo = this.props.filterThreadInfo.threadInfo;
     const beforeCheckStyles = { borderColor: `#${threadInfo.color}` };
     let afterCheck = null;
@@ -343,7 +343,7 @@
   +selected: boolean,
 };
 class Category extends React.PureComponent<CategoryProps> {
-  render() {
+  render(): React.Node {
     const beforeCheckStyles = { borderColor: 'white' };
     let afterCheck = null;
     if (this.props.selected) {
diff --git a/web/chat/chat-input-bar.react.js b/web/chat/chat-input-bar.react.js
--- a/web/chat/chat-input-bar.react.js
+++ b/web/chat/chat-input-bar.react.js
@@ -166,7 +166,7 @@
 
   static unassignedUploadIDs(
     pendingUploads: $ReadOnlyArray<PendingMultimediaUpload>,
-  ) {
+  ): string[] {
     return pendingUploads
       .filter(
         (pendingUpload: PendingMultimediaUpload) => !pendingUpload.messageID,
@@ -199,7 +199,7 @@
     this.props.inputState.removeReplyListener(this.focusAndUpdateText);
   }
 
-  render() {
+  render(): React.Node {
     const isMember = viewerIsMember(this.props.threadInfo);
     const canJoin = threadHasPermission(
       this.props.threadInfo,
@@ -540,7 +540,7 @@
     this.props.dispatchActionPromise(joinThreadActionTypes, this.joinAction());
   };
 
-  async joinAction() {
+  async joinAction(): Promise<ThreadJoinPayload> {
     const query = this.props.calendarQuery();
     return await this.props.joinThread({
       threadID: this.props.threadInfo.id,
diff --git a/web/chat/chat-message-list.react.js b/web/chat/chat-message-list.react.js
--- a/web/chat/chat-message-list.react.js
+++ b/web/chat/chat-message-list.react.js
@@ -107,7 +107,7 @@
     this.props.removeScrollToMessageListener(this.scrollToMessage);
   }
 
-  getSnapshotBeforeUpdate(prevProps: Props) {
+  getSnapshotBeforeUpdate(prevProps: Props): ?Snapshot {
     if (
       ChatMessageList.hasNewMessage(this.props, prevProps) &&
       this.messageContainer
@@ -118,7 +118,7 @@
     return null;
   }
 
-  static hasNewMessage(props: Props, prevProps: Props) {
+  static hasNewMessage(props: Props, prevProps: Props): boolean {
     const { messageListData } = props;
     if (!messageListData || messageListData.length === 0) {
       return false;
@@ -133,7 +133,7 @@
     );
   }
 
-  componentDidUpdate(prevProps: Props, prevState, snapshot: ?Snapshot) {
+  componentDidUpdate(prevProps: Props, prevState: State, snapshot: ?Snapshot) {
     const { messageListData } = this.props;
     const prevMessageListData = prevProps.messageListData;
 
@@ -180,14 +180,14 @@
     }
   }
 
-  static keyExtractor(item: ChatMessageItem) {
+  static keyExtractor(item: ChatMessageItem): string {
     if (item.itemType === 'loader') {
       return 'loader';
     }
     return messageKey(item.messageInfo);
   }
 
-  renderItem = item => {
+  renderItem = (item: ChatMessageItem): React.Node => {
     if (item.itemType === 'loader') {
       return (
         <div key="loader" className={css.loading}>
@@ -271,7 +271,7 @@
     return maxHeight;
   };
 
-  willMessageEditWindowOverflow(composedMessageID: string) {
+  willMessageEditWindowOverflow(composedMessageID: string): boolean {
     const { messageContainer } = this;
     if (!messageContainer) {
       return false;
@@ -305,7 +305,7 @@
     return messageBottom > containerBottom || messageTop < containerTop;
   }
 
-  render() {
+  render(): React.Node {
     const { messageListData, threadInfo, inputState, isEditState } = this.props;
     if (!messageListData) {
       return <div className={css.container} />;
@@ -353,7 +353,7 @@
     this.debounceEditModeAfterScrollToMessage();
   };
 
-  debounceEditModeAfterScrollToMessage = _debounce(() => {
+  debounceEditModeAfterScrollToMessage: () => void = _debounce(() => {
     if (this.state.scrollingEndCallback) {
       this.state.scrollingEndCallback();
     }
diff --git a/web/chat/chat-thread-list-item-menu.react.js b/web/chat/chat-thread-list-item-menu.react.js
--- a/web/chat/chat-thread-list-item-menu.react.js
+++ b/web/chat/chat-thread-list-item-menu.react.js
@@ -21,7 +21,7 @@
   const active = useThreadIsActive(threadInfo.id);
   const [menuVisible, setMenuVisible] = React.useState(false);
   const toggleMenu = React.useCallback(
-    event => {
+    (event: SyntheticEvent<HTMLButtonElement>) => {
       event.stopPropagation();
       setMenuVisible(!menuVisible);
     },
@@ -39,7 +39,7 @@
   );
 
   const onToggleUnreadStatusClicked = React.useCallback(
-    event => {
+    (event: SyntheticEvent<HTMLButtonElement>) => {
       event.stopPropagation();
       toggleUnreadStatus();
     },
diff --git a/web/chat/chat-thread-list.react.js b/web/chat/chat-thread-list.react.js
--- a/web/chat/chat-thread-list.react.js
+++ b/web/chat/chat-thread-list.react.js
@@ -41,7 +41,12 @@
   }
 };
 
-const renderItem = ({ index, data, style }) => {
+type RenderItemInput = {
+  +index: number,
+  +data: $ReadOnlyArray<Item>,
+  +style: CSSStyleDeclaration,
+};
+const renderItem: RenderItemInput => React.Node = ({ index, data, style }) => {
   let item;
   if (data[index].type === 'search') {
     item = <ChatThreadListSearch />;
@@ -129,7 +134,7 @@
       items.push({ type: 'empty' });
     }
 
-    const itemSize = index => {
+    const itemSize = (index: number) => {
       if (items[index].type === 'search') {
         return sizes.search;
       } else if (items[index].type === 'empty') {
diff --git a/web/chat/edit-text-message.react.js b/web/chat/edit-text-message.react.js
--- a/web/chat/edit-text-message.react.js
+++ b/web/chat/edit-text-message.react.js
@@ -98,7 +98,7 @@
   }, [background, updatePosition]);
 
   const preventCloseTab = React.useCallback(
-    event => {
+    (event: BeforeUnloadEvent) => {
       if (!isMessageEdited) {
         return null;
       }
diff --git a/web/chat/failed-send.react.js b/web/chat/failed-send.react.js
--- a/web/chat/failed-send.react.js
+++ b/web/chat/failed-send.react.js
@@ -79,7 +79,7 @@
     }
   }
 
-  render() {
+  render(): React.Node {
     return (
       <div className={css.failedSend}>
         <span className={css.deliveryFailed}>Delivery failed.</span>
diff --git a/web/chat/message-tooltip.react.js b/web/chat/message-tooltip.react.js
--- a/web/chat/message-tooltip.react.js
+++ b/web/chat/message-tooltip.react.js
@@ -179,7 +179,7 @@
   );
 
   const onEmojiSelect = React.useCallback(
-    emoji => {
+    (emoji: { +native: string, ... }) => {
       const reactionInput = emoji.native;
       sendReaction(reactionInput);
     },
diff --git a/web/chat/multimedia-message.react.js b/web/chat/multimedia-message.react.js
--- a/web/chat/multimedia-message.react.js
+++ b/web/chat/multimedia-message.react.js
@@ -27,7 +27,7 @@
   +inputState: ?InputState,
 };
 class MultimediaMessage extends React.PureComponent<Props> {
-  render() {
+  render(): React.Node {
     const { item, inputState } = this.props;
     invariant(
       item.messageInfo.type === messageTypes.IMAGES ||
diff --git a/web/chat/robotext-message.react.js b/web/chat/robotext-message.react.js
--- a/web/chat/robotext-message.react.js
+++ b/web/chat/robotext-message.react.js
@@ -108,7 +108,7 @@
   +dispatch: Dispatch,
 };
 class InnerThreadEntity extends React.PureComponent<InnerThreadEntityProps> {
-  render() {
+  render(): React.Node {
     return <a onClick={this.onClickThread}>{this.props.name}</a>;
   }
 
diff --git a/web/components/button.react.js b/web/components/button.react.js
--- a/web/components/button.react.js
+++ b/web/components/button.react.js
@@ -61,7 +61,7 @@
     style = buttonThemes.standard;
   }
 
-  const wrappedChildren = React.Children.map(children, child => {
+  const wrappedChildren = React.Children.map(children, (child: React.Node) => {
     if (typeof child === 'string' || typeof child === 'number') {
       return <span>{child}</span>;
     }
diff --git a/web/components/dropdown.react.js b/web/components/dropdown.react.js
--- a/web/components/dropdown.react.js
+++ b/web/components/dropdown.react.js
@@ -48,7 +48,7 @@
   }, [disabled, isOpen]);
 
   const handleSelection = React.useCallback(
-    selection => {
+    (selection: DropdownOption) => {
       setActiveSelection(selection.id);
       setIsOpen(false);
     },
diff --git a/web/components/menu.react.js b/web/components/menu.react.js
--- a/web/components/menu.react.js
+++ b/web/components/menu.react.js
@@ -102,7 +102,7 @@
   }, [closeMenu]);
 
   const onClickMenuCallback = React.useCallback(
-    e => {
+    (e: SyntheticEvent<HTMLButtonElement>) => {
       e.stopPropagation();
       setCurrentOpenMenu(ourSymbol.current);
     },
diff --git a/web/components/navigation-arrows.react.js b/web/components/navigation-arrows.react.js
--- a/web/components/navigation-arrows.react.js
+++ b/web/components/navigation-arrows.react.js
@@ -9,7 +9,8 @@
 import electron from '../electron.js';
 import history from '../router-history.js';
 
-const stopDoubleClickPropagation = e => e.stopPropagation();
+const stopDoubleClickPropagation = (e: SyntheticEvent<HTMLAnchorElement>) =>
+  e.stopPropagation();
 
 function NavigationArrows(): React.Node {
   const goBack = React.useCallback(
diff --git a/web/components/search.react.js b/web/components/search.react.js
--- a/web/components/search.react.js
+++ b/web/components/search.react.js
@@ -1,5 +1,6 @@
 // @flow
 
+import invariant from 'invariant';
 import * as React from 'react';
 
 import SWMansionIcon from 'lib/components/SWMansionIcon.react.js';
@@ -30,8 +31,10 @@
   }, [onChangeText, onClearText]);
 
   const onChange = React.useCallback(
-    event => {
-      onChangeText(event.target.value);
+    (event: SyntheticEvent<HTMLInputElement>) => {
+      const { target } = event;
+      invariant(target instanceof HTMLInputElement, 'target not input');
+      onChangeText(target.value);
     },
     [onChangeText],
   );
diff --git a/web/input/input-state-container.react.js b/web/input/input-state-container.react.js
--- a/web/input/input-state-container.react.js
+++ b/web/input/input-state-container.react.js
@@ -100,6 +100,9 @@
   type PendingMultimediaUpload,
   type TypeaheadState,
   InputStateContext,
+  type BaseInputState,
+  type TypeaheadInputState,
+  type InputState,
 } from './input-state.js';
 import { encryptFile } from '../media/encryption-utils.js';
 import { generateThumbHash } from '../media/image-utils.js';
@@ -172,7 +175,10 @@
     },
   };
   replyCallbacks: Array<(message: string) => void> = [];
-  pendingThreadCreations = new Map<string, Promise<string>>();
+  pendingThreadCreations: Map<string, Promise<string>> = new Map<
+    string,
+    Promise<string>,
+  >();
   // TODO: flip the switch
   // Note that this enables Blob service for encrypted media only
   useBlobServiceUploads = false;
@@ -181,7 +187,7 @@
   // sidebar, the sidebar gets created right away, but the message needs to wait
   // for the uploads to complete before sending. We use this Set to track the
   // message localIDs that need sidebarCreation: true.
-  pendingSidebarCreationMessageLocalIDs = new Set<string>();
+  pendingSidebarCreationMessageLocalIDs: Set<string> = new Set<string>();
 
   static reassignToRealizedThreads<T>(
     state: { +[threadID: string]: T },
@@ -200,7 +206,7 @@
     return updated ? newState : null;
   }
 
-  static getDerivedStateFromProps(props: Props, state: State) {
+  static getDerivedStateFromProps(props: Props, state: State): ?Partial<State> {
     const pendingUploads = InputStateContainer.reassignToRealizedThreads(
       state.pendingUploads,
       props,
@@ -224,7 +230,7 @@
     return stateUpdate;
   }
 
-  static completedMessageIDs(state: State) {
+  static completedMessageIDs(state: State): Set<string> {
     const completed = new Map();
     for (const threadID in state.pendingUploads) {
       const pendingUploads = state.pendingUploads[threadID];
@@ -404,7 +410,9 @@
     return threadInfoInsideCommunity(threadInfo, commStaffCommunity.id);
   }
 
-  async sendMultimediaMessage(messageInfo: RawMultimediaMessageInfo) {
+  async sendMultimediaMessage(
+    messageInfo: RawMultimediaMessageInfo,
+  ): Promise<void> {
     if (!threadIsPending(messageInfo.threadID)) {
       this.props.dispatchActionPromise(
         sendMultimediaMessageActionTypes,
@@ -564,74 +572,84 @@
     return threadCreationPromise;
   }
 
-  inputBaseStateSelector = _memoize((threadID: ?string) =>
-    createSelector(
-      (propsAndState: PropsAndState) =>
-        threadID ? propsAndState.pendingUploads[threadID] : null,
-      (propsAndState: PropsAndState) =>
-        threadID ? propsAndState.drafts[draftKeyFromThreadID(threadID)] : null,
-      (propsAndState: PropsAndState) =>
-        threadID ? propsAndState.textCursorPositions[threadID] : null,
-      (
-        pendingUploads: ?{ [localUploadID: string]: PendingMultimediaUpload },
-        draft: ?string,
-        textCursorPosition: ?number,
-      ) => {
-        let threadPendingUploads = [];
-        const assignedUploads = {};
-        if (pendingUploads) {
-          const [uploadsWithMessageIDs, uploadsWithoutMessageIDs] =
-            _partition('messageID')(pendingUploads);
-          threadPendingUploads = _sortBy('localID')(uploadsWithoutMessageIDs);
-          const threadAssignedUploads = _groupBy('messageID')(
-            uploadsWithMessageIDs,
-          );
-          for (const messageID in threadAssignedUploads) {
-            // lodash libdefs don't return $ReadOnlyArray
-            assignedUploads[messageID] = [...threadAssignedUploads[messageID]];
+  inputBaseStateSelector: (?string) => PropsAndState => BaseInputState =
+    _memoize((threadID: ?string) =>
+      createSelector(
+        (propsAndState: PropsAndState) =>
+          threadID ? propsAndState.pendingUploads[threadID] : null,
+        (propsAndState: PropsAndState) =>
+          threadID
+            ? propsAndState.drafts[draftKeyFromThreadID(threadID)]
+            : null,
+        (propsAndState: PropsAndState) =>
+          threadID ? propsAndState.textCursorPositions[threadID] : null,
+        (
+          pendingUploads: ?{ [localUploadID: string]: PendingMultimediaUpload },
+          draft: ?string,
+          textCursorPosition: ?number,
+        ) => {
+          let threadPendingUploads = [];
+          const assignedUploads = {};
+          if (pendingUploads) {
+            const [uploadsWithMessageIDs, uploadsWithoutMessageIDs] =
+              _partition('messageID')(pendingUploads);
+            threadPendingUploads = _sortBy('localID')(uploadsWithoutMessageIDs);
+            const threadAssignedUploads = _groupBy('messageID')(
+              uploadsWithMessageIDs,
+            );
+            for (const messageID in threadAssignedUploads) {
+              // lodash libdefs don't return $ReadOnlyArray
+              assignedUploads[messageID] = [
+                ...threadAssignedUploads[messageID],
+              ];
+            }
           }
-        }
-        return {
-          pendingUploads: threadPendingUploads,
-          assignedUploads,
-          draft: draft ?? '',
-          textCursorPosition: textCursorPosition ?? 0,
-          appendFiles: (threadInfo: ThreadInfo, files: $ReadOnlyArray<File>) =>
-            this.appendFiles(threadInfo, files),
-          cancelPendingUpload: (localUploadID: string) =>
-            this.cancelPendingUpload(threadID, localUploadID),
-          sendTextMessage: (
-            messageInfo: RawTextMessageInfo,
-            threadInfo: ThreadInfo,
-            parentThreadInfo: ?ThreadInfo,
-          ) => this.sendTextMessage(messageInfo, threadInfo, parentThreadInfo),
-          createMultimediaMessage: (localID: number, threadInfo: ThreadInfo) =>
-            this.createMultimediaMessage(localID, threadInfo),
-          setDraft: (newDraft: string) => this.setDraft(threadID, newDraft),
-          setTextCursorPosition: (newPosition: number) =>
-            this.setTextCursorPosition(threadID, newPosition),
-          messageHasUploadFailure: (localMessageID: string) =>
-            this.messageHasUploadFailure(assignedUploads[localMessageID]),
-          retryMultimediaMessage: (
-            localMessageID: string,
-            threadInfo: ThreadInfo,
-          ) =>
-            this.retryMultimediaMessage(
-              localMessageID,
-              threadInfo,
-              assignedUploads[localMessageID],
-            ),
-          addReply: (message: string) => this.addReply(message),
-          addReplyListener: this.addReplyListener,
-          removeReplyListener: this.removeReplyListener,
-          registerSendCallback: this.props.registerSendCallback,
-          unregisterSendCallback: this.props.unregisterSendCallback,
-        };
-      },
-    ),
-  );
+          return {
+            pendingUploads: threadPendingUploads,
+            assignedUploads,
+            draft: draft ?? '',
+            textCursorPosition: textCursorPosition ?? 0,
+            appendFiles: (
+              threadInfo: ThreadInfo,
+              files: $ReadOnlyArray<File>,
+            ) => this.appendFiles(threadInfo, files),
+            cancelPendingUpload: (localUploadID: string) =>
+              this.cancelPendingUpload(threadID, localUploadID),
+            sendTextMessage: (
+              messageInfo: RawTextMessageInfo,
+              threadInfo: ThreadInfo,
+              parentThreadInfo: ?ThreadInfo,
+            ) =>
+              this.sendTextMessage(messageInfo, threadInfo, parentThreadInfo),
+            createMultimediaMessage: (
+              localID: number,
+              threadInfo: ThreadInfo,
+            ) => this.createMultimediaMessage(localID, threadInfo),
+            setDraft: (newDraft: string) => this.setDraft(threadID, newDraft),
+            setTextCursorPosition: (newPosition: number) =>
+              this.setTextCursorPosition(threadID, newPosition),
+            messageHasUploadFailure: (localMessageID: string) =>
+              this.messageHasUploadFailure(assignedUploads[localMessageID]),
+            retryMultimediaMessage: (
+              localMessageID: string,
+              threadInfo: ThreadInfo,
+            ) =>
+              this.retryMultimediaMessage(
+                localMessageID,
+                threadInfo,
+                assignedUploads[localMessageID],
+              ),
+            addReply: (message: string) => this.addReply(message),
+            addReplyListener: this.addReplyListener,
+            removeReplyListener: this.removeReplyListener,
+            registerSendCallback: this.props.registerSendCallback,
+            unregisterSendCallback: this.props.unregisterSendCallback,
+          };
+        },
+      ),
+    );
 
-  typeaheadStateSelector = createSelector(
+  typeaheadStateSelector: PropsAndState => TypeaheadInputState = createSelector(
     (propsAndState: PropsAndState) => propsAndState.typeaheadState,
     (typeaheadState: TypeaheadState) => ({
       typeaheadState,
@@ -639,7 +657,10 @@
     }),
   );
 
-  inputStateSelector = createSelector(
+  inputStateSelector: ({
+    +inputBaseState: BaseInputState,
+    +typeaheadState: TypeaheadInputState,
+  }) => InputState = createSelector(
     state => state.inputBaseState,
     state => state.typeaheadState,
     (inputBaseState, typeaheadState) => ({
@@ -816,7 +837,7 @@
   uploadFiles(
     threadID: string,
     uploads: $ReadOnlyArray<PendingMultimediaUpload>,
-  ) {
+  ): Promise<mixed> {
     return Promise.all(
       uploads.map(upload => this.uploadFile(threadID, upload)),
     );
@@ -1447,7 +1468,7 @@
 
   messageHasUploadFailure(
     pendingUploads: ?$ReadOnlyArray<PendingMultimediaUpload>,
-  ) {
+  ): boolean {
     if (!pendingUploads) {
       return false;
     }
@@ -1563,7 +1584,7 @@
     );
   };
 
-  render() {
+  render(): React.Node {
     const { activeChatThreadID } = this.props;
 
     // we're going with two selectors as we want to avoid
diff --git a/web/input/input-state.js b/web/input/input-state.js
--- a/web/input/input-state.js
+++ b/web/input/input-state.js
@@ -55,15 +55,13 @@
   +accept: ?() => void,
 };
 
-// This type represents the input state for a particular thread
-export type InputState = {
+export type BaseInputState = {
   +pendingUploads: $ReadOnlyArray<PendingMultimediaUpload>,
   +assignedUploads: {
     [messageID: string]: $ReadOnlyArray<PendingMultimediaUpload>,
   },
   +draft: string,
   +textCursorPosition: number,
-  +typeaheadState: TypeaheadState,
   +appendFiles: (
     threadInfo: ThreadInfo,
     files: $ReadOnlyArray<File>,
@@ -77,7 +75,6 @@
   +createMultimediaMessage: (localID: number, threadInfo: ThreadInfo) => void,
   +setDraft: (draft: string) => void,
   +setTextCursorPosition: (newPosition: number) => void,
-  +setTypeaheadState: ($Shape<TypeaheadState>) => void,
   +messageHasUploadFailure: (localMessageID: string) => boolean,
   +retryMultimediaMessage: (
     localMessageID: string,
@@ -90,6 +87,17 @@
   +unregisterSendCallback: (() => mixed) => void,
 };
 
+export type TypeaheadInputState = {
+  +typeaheadState: TypeaheadState,
+  +setTypeaheadState: ($Shape<TypeaheadState>) => void,
+};
+
+// This type represents the input state for a particular thread
+export type InputState = {
+  ...BaseInputState,
+  ...TypeaheadInputState,
+};
+
 const InputStateContext: React.Context<?InputState> =
   React.createContext<?InputState>(null);
 
diff --git a/web/modals/history/history-entry.react.js b/web/modals/history/history-entry.react.js
--- a/web/modals/history/history-entry.react.js
+++ b/web/modals/history/history-entry.react.js
@@ -17,6 +17,7 @@
   type RestoreEntryInfo,
   type RestoreEntryResult,
   type CalendarQuery,
+  type RestoreEntryPayload,
 } from 'lib/types/entry-types.js';
 import type { LoadingStatus } from 'lib/types/loading-types.js';
 import type { ResolvedThreadInfo } from 'lib/types/thread-types.js';
@@ -49,7 +50,7 @@
 };
 
 class HistoryEntry extends React.PureComponent<Props> {
-  render() {
+  render(): React.Node {
     let deleted = null;
     if (this.props.entryInfo.deleted) {
       let restore = null;
@@ -133,7 +134,7 @@
     this.props.onClick(entryID);
   };
 
-  async restoreEntryAction() {
+  async restoreEntryAction(): Promise<RestoreEntryPayload> {
     const entryID = this.props.entryInfo.id;
     invariant(entryID, 'entry should have ID');
     const result = await this.props.restoreEntry({
diff --git a/web/modals/history/history-modal.react.js b/web/modals/history/history-modal.react.js
--- a/web/modals/history/history-modal.react.js
+++ b/web/modals/history/history-modal.react.js
@@ -71,7 +71,7 @@
   +revisions: $ReadOnlyArray<HistoryRevisionInfo>,
 };
 class HistoryModal extends React.PureComponent<Props, State> {
-  static defaultProps = { currentEntryID: null };
+  static defaultProps: Partial<Props> = { currentEntryID: null };
 
   constructor(props: Props) {
     super(props);
@@ -91,7 +91,7 @@
     }
   }
 
-  render() {
+  render(): React.Node {
     let allHistoryButton = null;
     if (this.state.mode === 'entry') {
       allHistoryButton = (
diff --git a/web/modals/search/message-search-modal.react.js b/web/modals/search/message-search-modal.react.js
--- a/web/modals/search/message-search-modal.react.js
+++ b/web/modals/search/message-search-modal.react.js
@@ -3,6 +3,7 @@
 import * as React from 'react';
 
 import { useModalContext } from 'lib/components/modal-provider.react.js';
+import type { ChatMessageInfoItem } from 'lib/selectors/chat-selectors.js';
 import type { ThreadInfo } from 'lib/types/thread-types.js';
 import { useResolvedThreadInfo } from 'lib/utils/entity-helpers.js';
 
@@ -40,7 +41,7 @@
   }, [setQuery, input, searchMessages, threadInfo.id]);
 
   const onKeyDown = React.useCallback(
-    event => {
+    (event: SyntheticKeyboardEvent<HTMLInputElement>) => {
       if (event.key === 'Enter') {
         onPressSearch();
       }
@@ -76,7 +77,7 @@
   }, [clearTooltip, possiblyLoadMoreMessages]);
 
   const renderItem = React.useCallback(
-    item => (
+    (item: ChatMessageInfoItem) => (
       <MessageResult
         key={item.messageInfo.id}
         item={item}
diff --git a/web/modals/threads/gallery/thread-settings-media-gallery.react.js b/web/modals/threads/gallery/thread-settings-media-gallery.react.js
--- a/web/modals/threads/gallery/thread-settings-media-gallery.react.js
+++ b/web/modals/threads/gallery/thread-settings-media-gallery.react.js
@@ -1,5 +1,6 @@
 // @flow
 
+import invariant from 'invariant';
 import * as React from 'react';
 
 import { useFetchThreadMedia } from 'lib/actions/thread-actions.js';
@@ -142,8 +143,9 @@
   }, [tab, mediaInfos, onClick]);
 
   const handleScroll = React.useCallback(
-    async event => {
+    async (event: SyntheticEvent<HTMLDivElement>) => {
       const container = event.target;
+      invariant(container instanceof HTMLDivElement, 'target not div');
       // Load more data when the user is within 1000 pixels of the end
       const buffer = 1000;
 
diff --git a/web/modals/threads/members/add-members-modal.react.js b/web/modals/threads/members/add-members-modal.react.js
--- a/web/modals/threads/members/add-members-modal.react.js
+++ b/web/modals/threads/members/add-members-modal.react.js
@@ -78,7 +78,7 @@
   const userSearchResultsWithENSNames = useENSNames(userSearchResults);
 
   const onSwitchUser = React.useCallback(
-    userID =>
+    (userID: string) =>
       setPendingUsersToAdd(users => {
         const newUsers = new Set(users);
         if (newUsers.has(userID)) {
diff --git a/web/modals/threads/members/member.react.js b/web/modals/threads/members/member.react.js
--- a/web/modals/threads/members/member.react.js
+++ b/web/modals/threads/members/member.react.js
@@ -44,7 +44,7 @@
   const roleName = roles.get(memberInfo.id)?.name;
 
   const onMenuChange = React.useCallback(
-    menuOpen => {
+    (menuOpen: boolean) => {
       if (menuOpen) {
         setOpenMenu(() => memberInfo.id);
       } else {
diff --git a/web/modals/threads/sidebars/sidebar.react.js b/web/modals/threads/sidebars/sidebar.react.js
--- a/web/modals/threads/sidebars/sidebar.react.js
+++ b/web/modals/threads/sidebars/sidebar.react.js
@@ -31,7 +31,7 @@
   const navigateToThread = useOnClickThread(threadInfo);
 
   const onClickThread = React.useCallback(
-    event => {
+    (event: SyntheticEvent<HTMLButtonElement>) => {
       popModal();
       navigateToThread(event);
     },
diff --git a/web/modals/threads/subchannels/subchannel.react.js b/web/modals/threads/subchannels/subchannel.react.js
--- a/web/modals/threads/subchannels/subchannel.react.js
+++ b/web/modals/threads/subchannels/subchannel.react.js
@@ -40,7 +40,7 @@
   const navigateToThread = useOnClickThread(threadInfo);
 
   const onClickThread = React.useCallback(
-    event => {
+    (event: SyntheticEvent<HTMLButtonElement>) => {
       popModal();
       navigateToThread(event);
     },
diff --git a/web/modals/update-modal.react.js b/web/modals/update-modal.react.js
--- a/web/modals/update-modal.react.js
+++ b/web/modals/update-modal.react.js
@@ -73,7 +73,7 @@
 
   React.useEffect(
     () =>
-      electron?.onNewVersionAvailable?.(version => {
+      electron?.onNewVersionAvailable?.((version: string) => {
         // On these versions we want to update immediately because there's
         // an issue if the user decides to update 10min after showing the modal
         if (electron?.version === '1.0.0' || electron?.version === '2.0.0') {
diff --git a/web/push-notif/push-notifs-handler.js b/web/push-notif/push-notifs-handler.js
--- a/web/push-notif/push-notifs-handler.js
+++ b/web/push-notif/push-notifs-handler.js
@@ -28,7 +28,7 @@
 
   React.useEffect(
     () =>
-      electron?.onDeviceTokenRegistered?.(token => {
+      electron?.onDeviceTokenRegistered?.((token: ?string) => {
         dispatchActionPromise(
           setDeviceTokenActionTypes,
           callSetDeviceToken(token),
@@ -41,20 +41,22 @@
 
   React.useEffect(
     () =>
-      electron?.onNotificationClicked?.(({ threadID }) => {
-        const convertedThreadID = convertNonPendingIDToNewSchema(
-          threadID,
-          ashoatKeyserverID,
-        );
-
-        const payload = {
-          chatMode: 'view',
-          activeChatThreadID: convertedThreadID,
-          tab: 'chat',
-        };
-
-        dispatch({ type: updateNavInfoActionType, payload });
-      }),
+      electron?.onNotificationClicked?.(
+        ({ threadID }: { +threadID: string }) => {
+          const convertedThreadID = convertNonPendingIDToNewSchema(
+            threadID,
+            ashoatKeyserverID,
+          );
+
+          const payload = {
+            chatMode: 'view',
+            activeChatThreadID: convertedThreadID,
+            tab: 'chat',
+          };
+
+          dispatch({ type: updateNavInfoActionType, payload });
+        },
+      ),
     [dispatch],
   );
 }
diff --git a/web/redux/focus-handler.react.js b/web/redux/focus-handler.react.js
--- a/web/redux/focus-handler.react.js
+++ b/web/redux/focus-handler.react.js
@@ -35,7 +35,7 @@
   const dispatch = useDispatch();
   const curWindowActive = useSelector(state => state.windowActive);
   const updateRedux = React.useCallback(
-    windowActive => {
+    (windowActive: boolean) => {
       if (windowActive === curWindowActive) {
         return;
       }
diff --git a/web/redux/initial-state-gate.js b/web/redux/initial-state-gate.js
--- a/web/redux/initial-state-gate.js
+++ b/web/redux/initial-state-gate.js
@@ -61,7 +61,7 @@
   const childFunction = React.useCallback(
     // This argument is passed from `PersistGate`. It means that the state is
     // rehydrated and we can start fetching the initial info.
-    bootstrapped => {
+    (bootstrapped: boolean) => {
       if (bootstrapped && initialStateLoaded) {
         return children;
       } else {
diff --git a/web/redux/persist.js b/web/redux/persist.js
--- a/web/redux/persist.js
+++ b/web/redux/persist.js
@@ -41,7 +41,7 @@
 declare var keyserverURL: string;
 
 const migrations = {
-  [1]: async state => {
+  [1]: async (state: any) => {
     const {
       primaryIdentityPublicKey,
       ...stateWithoutPrimaryIdentityPublicKey
@@ -56,7 +56,7 @@
       },
     };
   },
-  [2]: async state => {
+  [2]: async (state: AppState) => {
     return state;
   },
   [3]: async (state: AppState) => {
@@ -90,7 +90,7 @@
 
     return newState;
   },
-  [4]: async state => {
+  [4]: async (state: any) => {
     const { lastCommunicatedPlatformDetails, keyserverStore, ...rest } = state;
 
     return {
@@ -107,7 +107,7 @@
       },
     };
   },
-  [5]: async state => {
+  [5]: async (state: any) => {
     const databaseModule = await getDatabaseModule();
     const isDatabaseSupported = await databaseModule.isDatabaseSupported();
     if (!isDatabaseSupported) {
@@ -135,7 +135,7 @@
 
     return state;
   },
-  [6]: async state => ({
+  [6]: async (state: AppState) => ({
     ...state,
     integrityStore: { threadHashes: {}, threadHashingStatus: 'starting' },
   }),
@@ -166,11 +166,11 @@
       },
     };
   },
-  [8]: async state => ({
+  [8]: async (state: AppState) => ({
     ...state,
     globalThemeInfo: defaultGlobalThemeInfo,
   }),
-  [9]: async state => ({
+  [9]: async (state: AppState) => ({
     ...state,
     keyserverStore: {
       ...state.keyserverStore,
diff --git a/web/redux/visibility-handler.react.js b/web/redux/visibility-handler.react.js
--- a/web/redux/visibility-handler.react.js
+++ b/web/redux/visibility-handler.react.js
@@ -11,9 +11,12 @@
 function VisibilityHandler(): React.Node {
   const visibility = useVisibility();
   const [visible, setVisible] = React.useState(!visibility.hidden());
-  const onVisibilityChange = React.useCallback((event, state: string) => {
-    setVisible(state === 'visible');
-  }, []);
+  const onVisibilityChange = React.useCallback(
+    (event: mixed, state: string) => {
+      setVisible(state === 'visible');
+    },
+    [],
+  );
   React.useEffect(() => {
     const listener = visibility.change(onVisibilityChange);
     return () => {
@@ -24,7 +27,7 @@
   const dispatch = useDispatch();
   const curForeground = useIsAppForegrounded();
   const updateRedux = React.useCallback(
-    foreground => {
+    (foreground: boolean) => {
       if (foreground === curForeground) {
         return;
       }
diff --git a/web/settings/password-change-modal.js b/web/settings/password-change-modal.js
--- a/web/settings/password-change-modal.js
+++ b/web/settings/password-change-modal.js
@@ -56,7 +56,7 @@
     this.newPasswordInput.focus();
   }
 
-  render() {
+  render(): React.Node {
     let errorMsg;
     if (this.state.errorMessage) {
       errorMsg = (
@@ -188,7 +188,7 @@
     );
   };
 
-  async changeUserSettingsAction() {
+  async changeUserSettingsAction(): Promise<void> {
     try {
       await this.props.changeUserPassword({
         updatedFields: {
diff --git a/web/settings/tunnelbroker-test.react.js b/web/settings/tunnelbroker-test.react.js
--- a/web/settings/tunnelbroker-test.react.js
+++ b/web/settings/tunnelbroker-test.react.js
@@ -25,7 +25,7 @@
   const messageInput = React.useRef(null);
 
   const onSubmit = React.useCallback(
-    async event => {
+    async (event: SyntheticEvent<HTMLButtonElement>) => {
       event.preventDefault();
 
       setLoading(true);
diff --git a/web/utils/tooltip-action-utils.js b/web/utils/tooltip-action-utils.js
--- a/web/utils/tooltip-action-utils.js
+++ b/web/utils/tooltip-action-utils.js
@@ -410,7 +410,7 @@
   }, [messageTimestamp, tooltipActions]);
 
   const createMessageTooltip = React.useCallback(
-    tooltipPositionStyle => (
+    (tooltipPositionStyle: TooltipPositionStyle) => (
       <MessageTooltip
         actions={tooltipActions}
         messageTimestamp={messageTimestamp}
diff --git a/web/utils/typeahead-utils.js b/web/utils/typeahead-utils.js
--- a/web/utils/typeahead-utils.js
+++ b/web/utils/typeahead-utils.js
@@ -75,14 +75,21 @@
     caretLeftOffset,
   };
 }
-export type GetTypeaheadTooltipActionsParams<SuggestionItemType> = {
+type MentionTypeaheadSharedParams = {
   +inputStateDraft: string,
   +inputStateSetDraft: (draft: string) => mixed,
   +inputStateSetTextCursorPosition: (newPosition: number) => mixed,
-  +suggestions: $ReadOnlyArray<SuggestionItemType>,
   +textBeforeAtSymbol: string,
   +query: string,
 };
+export type GetTypeaheadTooltipActionsParams<SuggestionItemType> = {
+  ...MentionTypeaheadSharedParams,
+  +suggestions: $ReadOnlyArray<SuggestionItemType>,
+};
+export type MentionTypeaheadTooltipActionExecuteHandlerParams = {
+  ...MentionTypeaheadSharedParams,
+  +mentionText: string,
+};
 function mentionTypeaheadTooltipActionExecuteHandler({
   textBeforeAtSymbol,
   inputStateDraft,
@@ -90,7 +97,7 @@
   mentionText,
   inputStateSetDraft,
   inputStateSetTextCursorPosition,
-}) {
+}: MentionTypeaheadTooltipActionExecuteHandlerParams) {
   const { newText, newSelectionStart } = getNewTextAndSelection(
     textBeforeAtSymbol,
     inputStateDraft,