feat(packages/excalidraw): tweak and expose more API around state and lifecycle (#10939)

packages/excalidraw/CHANGELOG.md

@@ -18,22 +18,13 @@ Please add the latest change on the top under the correct section.
 ### Breaking changes
 
 - Renamed the `excalidrawAPI` prop to `onExcalidrawAPI`.
+  - `onExcalidrawAPI` is now called on mount (instead of during constructor), and later on unmount (with `null` value). The API may be removed altogether in the future (you can use `onMount` & `onUmount` to manage the `ExcalidrawAPI` object (e.g. to cache it to a global state), already).
 
 ### Features
 
-- Added `onMount` and `onInitialize` props. `onMount` receives `{ excalidrawAPI, container }` once the editor root is mounted, and `onInitialize` fires once the initial scene has loaded.
+- Added `ExcalidrawAPI.isDestroyed` flag. Set to `true` once the editor unmounts. Calling any `get*` method, `onStateChange`, or `onEvent` on a destroyed API instance will throw in development and `console.error` in production. The `ExcalidrawAPI` will be reset to `null` on umount, but to be extra safe, you should check `ExcalidrawAPI.isDestroyed` before calling these methods to guard against subtle race conditions in your code.
 
-  ```tsx
-  <Excalidraw
-    onMount={({ excalidrawAPI, container }) => {
-      console.log(container);
-      excalidrawAPI.scrollToContent();
-    }}
-    onInitialize={(api) => {
-      api.refresh();
-    }}
-  />
-  ```
+- Added `onMount`, `onInitialize`, and `onUnmount` props. `onMount` receives `{ excalidrawAPI, container }` once the editor root is mounted. `onInitialize` fires once the initial scene has loaded. `onUnmount` fires just before unmounting.
 
 - Same events are also accessible imperatively through `api.onEvent(...)`.
 
@@ -41,7 +32,6 @@ Please add the latest change on the top under the correct section.
   <Excalidraw
     onExcalidrawAPI={(api) => {
       api.onEvent("editor:mount", ({ excalidrawAPI, container }) => {
-        excalidrawAPI.scrollToContent();
         console.log(container);
       });
 
@@ -54,7 +44,9 @@ Please add the latest change on the top under the correct section.
 
   Note that in future releases, most, if not all, `excalidrawAPI.on*` subscriptions will be removed in favor of `excalidrawAPI.onEvent(name)`.
 
-- Exported `ExcalidrawAPIProvider`, `useExcalidrawAPI`, and `useAppStateValue` from the package entrypoint. The imperative API also now exposes `onStateChange`.
+- Also added `"editor:unmount"` lifecycle event, only accessible via `api.onEvent("editor:unmount")`.
+
+- Exported `<ExcalidrawAPIProvider/>`, `useExcalidrawAPI()`, `useAppStateValue(prop | props | selectorFunction)`, and `useOnExcalidrawStateChange(prop | props | selectorFunction, callback)` from the package. The imperative API also now exposes `onStateChange(prop | props | selectorFunction, callback?)`, and `onEvent(name, callback)`.
 
   ```tsx
   <ExcalidrawAPIProvider>
@@ -63,6 +55,9 @@ Please add the latest change on the top under the correct section.
   </ExcalidrawAPIProvider>;
 
   function Logger() {
+    // initially null before the ExcalidrawAPIProvider initializes ater
+    // <Excalidraw/> renders
+    // When <Excalidraw/> unmounts, is reset back to null
     const api = useExcalidrawAPI();
 
     useAppStateValue("viewModeEnabled", (viewModeEnabled) => {

packages/excalidraw/components/App.tsx

@@ -517,6 +517,7 @@ EditorInterfaceContext.displayName = "EditorInterfaceContext";
 const editorLifecycleEventBehavior = {
   "editor:mount": { cardinality: "once", replay: "last" },
   "editor:initialize": { cardinality: "once", replay: "last" },
+  "editor:unmount": { cardinality: "once", replay: "last" },
 } as const;
 
 export const ExcalidrawContainerContext = React.createContext<{
@@ -556,7 +557,7 @@ export const ExcalidrawAPIContext =
 ExcalidrawAPIContext.displayName = "ExcalidrawAPIContext";
 
 export const ExcalidrawAPISetContext = React.createContext<
-  ((api: ExcalidrawImperativeAPI) => void) | null
+  ((api: ExcalidrawImperativeAPI | null) => void) | null
 >(null);
 ExcalidrawAPISetContext.displayName = "ExcalidrawAPISetContext";
 
@@ -731,6 +732,50 @@ class App extends React.Component<AppProps, AppState> {
 
   api: ExcalidrawImperativeAPI;
 
+  private createExcalidrawAPI(): ExcalidrawImperativeAPI {
+    const api: ExcalidrawImperativeAPI = {
+      isDestroyed: false,
+      updateScene: this.updateScene,
+      applyDeltas: this.applyDeltas,
+      mutateElement: this.mutateElement,
+      updateLibrary: this.library.updateLibrary,
+      addFiles: this.addFiles,
+      resetScene: this.resetScene,
+      getSceneElementsIncludingDeleted: this.getSceneElementsIncludingDeleted,
+      getSceneElementsMapIncludingDeleted:
+        this.getSceneElementsMapIncludingDeleted,
+      history: {
+        clear: this.resetHistory,
+      },
+      scrollToContent: this.scrollToContent,
+      getSceneElements: this.getSceneElements,
+      getAppState: () => this.state,
+      getFiles: () => this.files,
+      getName: this.getName,
+      registerAction: (action: Action) => {
+        this.actionManager.registerAction(action);
+      },
+      refresh: this.refresh,
+      setToast: this.setToast,
+      id: this.id,
+      setActiveTool: this.setActiveTool,
+      setCursor: this.setCursor,
+      resetCursor: this.resetCursor,
+      getEditorInterface: () => this.editorInterface,
+      updateFrameRendering: this.updateFrameRendering,
+      toggleSidebar: this.toggleSidebar,
+      onChange: (cb) => this.onChangeEmitter.on(cb),
+      onIncrement: (cb) => this.store.onStoreIncrementEmitter.on(cb),
+      onPointerDown: (cb) => this.onPointerDownEmitter.on(cb),
+      onPointerUp: (cb) => this.onPointerUpEmitter.on(cb),
+      onScrollChange: (cb) => this.onScrollChangeEmitter.on(cb),
+      onUserFollow: (cb) => this.onUserFollowEmitter.on(cb),
+      onStateChange: this.onStateChange,
+      onEvent: this.onEvent,
+    };
+    return api;
+  }
+
   constructor(props: AppProps) {
     super(props);
     const defaultAppState = getDefaultAppState();
@@ -791,47 +836,11 @@ class App extends React.Component<AppProps, AppState> {
     this.actionManager.registerAction(createUndoAction(this.history));
     this.actionManager.registerAction(createRedoAction(this.history));
 
-    this.api = {
-      updateScene: this.updateScene,
-      applyDeltas: this.applyDeltas,
-      mutateElement: this.mutateElement,
-      updateLibrary: this.library.updateLibrary,
-      addFiles: this.addFiles,
-      resetScene: this.resetScene,
-      getSceneElementsIncludingDeleted: this.getSceneElementsIncludingDeleted,
-      getSceneElementsMapIncludingDeleted:
-        this.getSceneElementsMapIncludingDeleted,
-      history: {
-        clear: this.resetHistory,
-      },
-      scrollToContent: this.scrollToContent,
-      getSceneElements: this.getSceneElements,
-      getAppState: () => this.state,
-      getFiles: () => this.files,
-      getName: this.getName,
-      registerAction: (action: Action) => {
-        this.actionManager.registerAction(action);
-      },
-      refresh: this.refresh,
-      setToast: this.setToast,
-      id: this.id,
-      setActiveTool: this.setActiveTool,
-      setCursor: this.setCursor,
-      resetCursor: this.resetCursor,
-      getEditorInterface: () => this.editorInterface,
-      updateFrameRendering: this.updateFrameRendering,
-      toggleSidebar: this.toggleSidebar,
-      onChange: (cb) => this.onChangeEmitter.on(cb),
-      onIncrement: (cb) => this.store.onStoreIncrementEmitter.on(cb),
-      onPointerDown: (cb) => this.onPointerDownEmitter.on(cb),
-      onPointerUp: (cb) => this.onPointerUpEmitter.on(cb),
-      onScrollChange: (cb) => this.onScrollChangeEmitter.on(cb),
-      onUserFollow: (cb) => this.onUserFollowEmitter.on(cb),
-      onStateChange: this.onStateChange,
-      onEvent: this.onEvent,
-    } as const;
-
-    props.onExcalidrawAPI?.(this.api);
+    // in case internal editor APIs call this early, otherwise we need
+    // to construct this in componentDidMount because componentWillUnmount
+    // will invalidate it (so in StrictMode, doing this in constructor alone
+    // would be a problem)
+    this.api = this.createExcalidrawAPI();
   }
 
   updateEditorAtom = <Value, Args extends unknown[], Result>(
@@ -3003,6 +3012,8 @@ class App extends React.Component<AppProps, AppState> {
 
   public async componentDidMount() {
     this.unmounted = false;
+    this.api = this.createExcalidrawAPI();
+
     this.excalidrawContainerValue.container =
       this.excalidrawContainerRef.current;
 
@@ -3089,10 +3100,35 @@ class App extends React.Component<AppProps, AppState> {
 
     this.editorLifecycleEvents.emit("editor:mount", mountPayload);
     this.props.onMount?.(mountPayload);
+    this.props.onExcalidrawAPI?.(this.api);
   }
 
   public componentWillUnmount() {
+    // we're recreating the api object reference so that the
+    // <ExcalidrawAPIContext.Provider/> picks up on it
+    this.api = { ...this.api, isDestroyed: true };
+
+    for (const key of Object.keys(this.api) as (keyof typeof this.api)[]) {
+      if (
+        (key.startsWith("get") ||
+          key === "onStateChange" ||
+          key === "onEvent") &&
+        typeof this.api[key] === "function"
+      ) {
+        (this.api as any)[key] = () => {
+          throw new Error(
+            "ExcalidrawAPI is no longer usable after the editor has been unmounted and will return invalid/empty data. You should check for `ExcalidrawAPI.isDestroyed` before calling get* methods on subscribing to state/event changes.",
+          );
+        };
+      }
+    }
+
+    this.editorLifecycleEvents.emit("editor:unmount");
+    this.props.onUnmount?.();
+    this.props.onExcalidrawAPI?.(null);
+
     (window as any).launchQueue?.setConsumer(() => {});
+
     this.renderer.destroy();
     this.scene.destroy();
     this.scene = new Scene();

packages/excalidraw/hooks/useAppStateValue.ts

@@ -6,6 +6,51 @@ import { getDefaultAppState } from "../appState";
 
 import type { AppState } from "../types";
 
+type AppStateSelector =
+  | keyof AppState
+  | (keyof AppState)[]
+  | ((appState: AppState) => unknown);
+
+const getSelectedValue = (appState: AppState, selector: AppStateSelector) => {
+  if (typeof selector === "function") {
+    return selector(appState);
+  }
+  if (Array.isArray(selector)) {
+    return appState;
+  }
+  return appState[selector];
+};
+
+const getLatestValue = (
+  api: ReturnType<typeof useExcalidrawAPI>,
+  selector: AppStateSelector,
+  _internal: boolean,
+) => {
+  if (api?.isDestroyed) {
+    return;
+  }
+
+  let appState = api?.getAppState();
+  if (!appState) {
+    if (!_internal) {
+      return undefined;
+    }
+
+    console.warn(
+      "useAppStateValue: excalidrawAPI not defined yet for internal component while it should always be defined. Are you sure you're rendering inside of <Excalidraw/> component tree?",
+    );
+    // fall back in case there's a bug so we don't break the app
+    // (internal components using this internal useAppStateValue expect
+    //  non-undefined values on init)
+    appState = Object.assign(
+      { width: 0, height: 0, offsetLeft: 0, offsetTop: 0 },
+      getDefaultAppState(),
+    );
+  }
+
+  return getSelectedValue(appState, selector);
+};
+
 /**
  * Subscribes to specific appState changes. The component re-renders
  * only when the specified prop(s) change — not on every appState update.
@@ -19,92 +64,109 @@ import type { AppState } from "../types";
  *  - `(keyof AppState)[]` → whole `AppState`
  *  - selector function → selector's return type `T`
  *
- * Calls the optional callback with the latest value on every change (not called
- * on initial render).
- *
  * If excalidrawAPI is not ready yet (host apps), hook is rerendered with latest
  * value once available.
  */
 export function useAppStateValue<K extends keyof AppState>(
   prop: K,
-  callback?: (value: AppState[K], appState: AppState) => void,
   _internal?: boolean,
 ): AppState[K];
 export function useAppStateValue(
   props: (keyof AppState)[],
-  callback?: (props: AppState, appState: AppState) => void,
   _internal?: boolean,
 ): AppState;
 export function useAppStateValue<T>(
   selector: (appState: AppState) => T,
-  callback?: (value: T, appState: AppState) => void,
   _internal?: boolean,
 ): T;
 export function useAppStateValue(
-  selector:
-    | keyof AppState
-    | (keyof AppState)[]
-    | ((appState: AppState) => unknown),
-  callback?: (value: any, appState: AppState) => void,
+  selector: AppStateSelector,
   _internal: boolean = true,
 ): unknown {
   const api = useExcalidrawAPI();
+  const [, rerender] = useState(0);
 
-  const getLatestValue = () => {
-    let appState = api?.getAppState();
-    if (!appState) {
-      if (!_internal) {
-        return undefined;
-      }
-      console.warn(
-        "useAppStateValue: excalidrawAPI not defined yet for internal component in which case it should always be defined. Are you sure you're rendering inside of <Excalidraw/> component tree?",
-      );
-      // fall back in case there's a bug so we don't break the app
-      // (internal components using this internal useAppStateValue expect
-      //  non-undefined values on init)
-      appState = Object.assign(
-        { width: 0, height: 0, offsetLeft: 0, offsetTop: 0 },
-        getDefaultAppState(),
-      );
-    }
-    if (typeof selector === "function") {
-      return selector(appState);
-    }
-    if (Array.isArray(selector)) {
-      return appState;
-    }
-    return appState[selector];
-  };
-
-  const [value, setValue] = useState<unknown>(getLatestValue);
-
-  const stateRef = useRef({
-    selector,
-    callback,
-    isInitialized: !!api,
-    latestValue: value,
-  });
+  const stateRef = useRef<{
+    selector: AppStateSelector;
+    isInitialized: boolean;
+    latestValue: unknown;
+  } | null>(null);
+  if (!stateRef.current) {
+    stateRef.current = {
+      selector,
+      isInitialized: !!api,
+      latestValue: getLatestValue(api, selector, _internal),
+    };
+  }
   stateRef.current.selector = selector;
-  stateRef.current.callback = callback;
-  if (!stateRef.current.isInitialized && api) {
+  if (!stateRef.current.isInitialized && api && !api.isDestroyed) {
     stateRef.current.isInitialized = true;
-    stateRef.current.latestValue = getLatestValue();
+    stateRef.current.latestValue = getLatestValue(api, selector, _internal);
   }
 
   useEffect(() => {
-    if (!api) {
+    const currentStateRef = stateRef.current;
+    if (!api || api.isDestroyed || !currentStateRef) {
       return;
     }
 
-    return api.onStateChange(
-      stateRef.current.selector,
-      (newValue: any, state: AppState) => {
-        stateRef.current.latestValue = newValue;
-        stateRef.current.callback?.(newValue, state);
-        setValue(newValue);
-      },
-    );
+    return api.onStateChange(currentStateRef.selector, (newValue: any) => {
+      currentStateRef.latestValue = newValue;
+      rerender((value) => value + 1);
+    });
   }, [api]);
 
   return stateRef.current.latestValue;
 }
+
+/**
+ * Subscribes to specific appState changes without causing component rerenders.
+ *
+ * The callback is called on every matching change, but also on initial render
+ * so you can initialize your state.
+ */
+export function useOnAppStateChange<K extends keyof AppState>(
+  prop: K,
+  callback: (value: AppState[K], appState: AppState) => void,
+): undefined;
+export function useOnAppStateChange(
+  props: (keyof AppState)[],
+  callback: (props: AppState, appState: AppState) => void,
+): undefined;
+export function useOnAppStateChange<T>(
+  selector: (appState: AppState) => T,
+  callback: (value: T, appState: AppState) => void,
+): undefined;
+export function useOnAppStateChange(
+  selector: AppStateSelector,
+  callback: (value: any, appState: AppState) => void,
+): undefined {
+  const api = useExcalidrawAPI();
+
+  const stateRef = useRef({
+    selector,
+    callback,
+  });
+  stateRef.current.selector = selector;
+  stateRef.current.callback = callback;
+
+  useEffect(() => {
+    if (!api || api.isDestroyed) {
+      return;
+    }
+
+    stateRef.current.callback(
+      getLatestValue(api, stateRef.current.selector, true),
+      api.getAppState(),
+    );
+
+    return api.onStateChange(
+      stateRef.current.selector,
+      (newValue: any, state: AppState) => {
+        stateRef.current.callback(newValue, state);
+      },
+    );
+  }, [api]);
+
+  return undefined;
+}

packages/excalidraw/index.tsx

@@ -1,4 +1,10 @@
-import React, { useCallback, useContext, useEffect, useState } from "react";
+import React, {
+  useCallback,
+  useContext,
+  useEffect,
+  useRef,
+  useState,
+} from "react";
 
 import { DEFAULT_UI_OPTIONS, isShallowEqual } from "@excalidraw/common";
 
@@ -12,7 +18,10 @@ import LiveCollaborationTrigger from "./components/live-collaboration/LiveCollab
 import MainMenu from "./components/main-menu/MainMenu";
 import WelcomeScreen from "./components/welcome-screen/WelcomeScreen";
 import { defaultLang } from "./i18n";
-import { useAppStateValue as _useAppStateValue } from "./hooks/useAppStateValue";
+import {
+  useAppStateValue as _useAppStateValue,
+  useOnAppStateChange as _useOnAppStateChange,
+} from "./hooks/useAppStateValue";
 import { EditorJotaiProvider, editorJotaiStore } from "./editor-jotai";
 import polyfill from "./polyfill";
 
@@ -31,8 +40,8 @@ polyfill();
 
 /**
  * Stateless provider that allows `useExcalidrawAPI()` (and hooks built
- * on it, such as `useAppStateValue()`) to work outside the <Excalidraw>
- * component tree.
+ * on it, such as `useAppStateValue()` and `useOnAppStateChange()`) to work
+ * outside the <Excalidraw> component tree.
  */
 export const ExcalidrawAPIProvider = ({
   children,
@@ -57,6 +66,7 @@ const ExcalidrawBase = (props: ExcalidrawProps) => {
     initialData,
     onExcalidrawAPI,
     onMount,
+    onUnmount,
     onInitialize,
     isCollaborating = false,
     onPointerUpdate,
@@ -119,12 +129,16 @@ const ExcalidrawBase = (props: ExcalidrawProps) => {
   }
 
   const setExcalidrawAPI = useContext(ExcalidrawAPISetContext);
+
+  const onExcalidrawAPIRef = useRef(onExcalidrawAPI);
+  onExcalidrawAPIRef.current = onExcalidrawAPI;
+
   const handleExcalidrawAPI = useCallback(
-    (api: ExcalidrawImperativeAPI) => {
+    (api: ExcalidrawImperativeAPI | null) => {
       setExcalidrawAPI?.(api);
-      onExcalidrawAPI?.(api);
+      onExcalidrawAPIRef.current?.(api);
     },
-    [onExcalidrawAPI, setExcalidrawAPI],
+    [setExcalidrawAPI],
   );
 
   useEffect(() => {
@@ -162,6 +176,7 @@ const ExcalidrawBase = (props: ExcalidrawProps) => {
           initialData={initialData}
           onExcalidrawAPI={handleExcalidrawAPI}
           onMount={onMount}
+          onUnmount={onUnmount}
           onInitialize={onInitialize}
           isCollaborating={isCollaborating}
           onPointerUpdate={onPointerUpdate}
@@ -378,7 +393,7 @@ export {
 } from "./charts";
 
 // -----------------------------------------------------------------------------
-// useAppStateValue() wrapper for host apps for the return type to reflect the
+// useExcalidrawStateValue() wrapper for host apps for the return type to reflect the
 // the potentially `undefined` value for initial render before the excalidrawAPI
 // is ready.
 //
@@ -388,25 +403,23 @@ export {
  * @param prop - appState prop(s) to subscribe to, or a selector function.
  * NOTE `prop/selector` is memoized and will not change after initial render
  */
-export function useAppStateValue<K extends keyof AppState>(
+export function useExcalidrawStateValue<K extends keyof AppState>(
   prop: K,
-  callback?: (value: AppState[K], appState: AppState) => void,
 ): AppState[K] | undefined;
-export function useAppStateValue<T extends keyof AppState>(
+export function useExcalidrawStateValue<T extends keyof AppState>(
   props: T[],
-  callback?: (values: AppState, appState: AppState) => void,
 ): AppState | undefined;
-export function useAppStateValue<T>(
+export function useExcalidrawStateValue<T>(
   selector: (appState: AppState) => T,
-  callback?: (value: T, appState: AppState) => void,
 ): T | undefined;
-export function useAppStateValue(
+export function useExcalidrawStateValue(
   selector:
     | keyof AppState
     | (keyof AppState)[]
     | ((appState: AppState) => unknown),
-  callback?: (value: any, appState: AppState) => void,
 ) {
-  return _useAppStateValue(selector as any, callback, false);
+  return _useAppStateValue(selector as any, false);
 }
 // -----------------------------------------------------------------------------
+
+export { _useOnAppStateChange as useOnExcalidrawStateChange };

packages/excalidraw/tests/appStateHooks.test.tsx

@@ -0,0 +1,111 @@
+import { act, cleanup, render, screen } from "@testing-library/react";
+import { vi } from "vitest";
+
+import { getDefaultAppState } from "../appState";
+import { ExcalidrawAPIContext } from "../components/App";
+import { AppStateObserver } from "../components/AppStateObserver";
+import {
+  useAppStateValue,
+  useOnAppStateChange,
+} from "../hooks/useAppStateValue";
+
+import type { AppState, ExcalidrawImperativeAPI } from "../types";
+
+const createAppState = (): AppState => ({
+  ...getDefaultAppState(),
+  width: 0,
+  height: 0,
+  offsetLeft: 0,
+  offsetTop: 0,
+});
+
+const createMockAPI = (initialState: AppState) => {
+  let state = initialState;
+  const observer = new AppStateObserver(() => state);
+
+  return {
+    api: {
+      isDestroyed: false,
+      getAppState: () => state,
+      onStateChange: observer.onStateChange,
+    } as Pick<
+      ExcalidrawImperativeAPI,
+      "isDestroyed" | "getAppState" | "onStateChange"
+    > as ExcalidrawImperativeAPI,
+    updateAppState: (partial: Partial<AppState>) => {
+      const prevState = state;
+      state = { ...state, ...partial };
+      observer.flush(prevState);
+    },
+  };
+};
+
+describe("app state hooks", () => {
+  afterEach(() => {
+    cleanup();
+  });
+
+  it("useAppStateValue rerenders when the selected value changes", () => {
+    const renderSpy = vi.fn();
+    const { api, updateAppState } = createMockAPI(createAppState());
+
+    const ValueConsumer = () => {
+      const value = useAppStateValue("viewModeEnabled");
+      renderSpy(value);
+      return <div data-testid="value">{String(value)}</div>;
+    };
+
+    render(
+      <ExcalidrawAPIContext.Provider value={api}>
+        <ValueConsumer />
+      </ExcalidrawAPIContext.Provider>,
+    );
+
+    expect(screen.getByTestId("value").textContent).toBe("false");
+    expect(renderSpy).toHaveBeenCalledTimes(1);
+
+    act(() => {
+      updateAppState({ viewModeEnabled: true });
+    });
+
+    expect(screen.getByTestId("value").textContent).toBe("true");
+    expect(renderSpy).toHaveBeenCalledTimes(2);
+  });
+
+  it("useOnAppStateChange notifies without rerendering", () => {
+    const renderSpy = vi.fn();
+    const callback = vi.fn();
+    const { api, updateAppState } = createMockAPI(createAppState());
+
+    const ChangeConsumer = () => {
+      const value = useOnAppStateChange("viewModeEnabled", callback);
+      renderSpy(value);
+      return <div data-testid="value">{String(value)}</div>;
+    };
+
+    render(
+      <ExcalidrawAPIContext.Provider value={api}>
+        <ChangeConsumer />
+      </ExcalidrawAPIContext.Provider>,
+    );
+
+    expect(screen.getByTestId("value").textContent).toBe("undefined");
+    expect(renderSpy).toHaveBeenCalledTimes(1);
+    expect(callback).toHaveBeenCalledTimes(1);
+    expect(callback).toHaveBeenCalledWith(
+      false,
+      expect.objectContaining({ viewModeEnabled: false }),
+    );
+
+    act(() => {
+      updateAppState({ viewModeEnabled: true });
+    });
+
+    expect(renderSpy).toHaveBeenCalledTimes(1);
+    expect(callback).toHaveBeenCalledTimes(2);
+    expect(callback).toHaveBeenLastCalledWith(
+      true,
+      expect.objectContaining({ viewModeEnabled: true }),
+    );
+  });
+});

packages/excalidraw/tests/packages/events.test.tsx

@@ -41,13 +41,15 @@ describe("event callbacks", () => {
 
     await render(
       <Excalidraw
-        onExcalidrawAPI={(api) =>
-          lifecyclePromise.resolve({
-            api: api as ExcalidrawImperativeAPI,
-            mount: api.onEvent("editor:mount"),
-            initialize: api.onEvent("editor:initialize"),
-          })
-        }
+        onExcalidrawAPI={(api) => {
+          if (api) {
+            lifecyclePromise.resolve({
+              api,
+              mount: api.onEvent("editor:mount"),
+              initialize: api.onEvent("editor:initialize"),
+            });
+          }
+        }}
       />,
     );
 

packages/excalidraw/types.ts

@@ -573,11 +573,15 @@ export interface ExcalidrawProps {
    * Invoked as soon as the Excalidraw API is available
    * NOTE editor is not yet mounted, and state is not yet initialized
    */
-  onExcalidrawAPI?: (api: ExcalidrawImperativeAPI) => void;
+  onExcalidrawAPI?: (api: ExcalidrawImperativeAPI | null) => void;
   /**
    * Invoked once the editor root is mounted.
    */
   onMount?: (payload: ExcalidrawMountPayload) => void;
+  /**
+   * Invoked when the editor root is unmounted.
+   */
+  onUnmount?: () => void;
   /**
    * Invoked once the initial scene is loaded.
    */
@@ -907,9 +911,12 @@ export type ExcalidrawMountPayload = {
 export type ExcalidrawImperativeAPIEventMap = {
   "editor:mount": [payload: ExcalidrawMountPayload];
   "editor:initialize": [api: ExcalidrawImperativeAPI];
+  "editor:unmount": [];
 };
 
 export interface ExcalidrawImperativeAPI {
+  /** Whether the editor has been unmounted and the API is no longer usable. */
+  isDestroyed: boolean;
   updateScene: InstanceType<typeof App>["updateScene"];
   applyDeltas: InstanceType<typeof App>["applyDeltas"];
   mutateElement: InstanceType<typeof App>["mutateElement"];