Add ScrollTimeline Polyfill for Swipe Recognizer using a new CustomTimeline protocol (#33501)

The React API is just that we now accept this protocol as an alternative
to a native `AnimationTimeline` to be passed to
`startGestureTransition`. This is specifically the DOM version.

```js
interface CustomTimeline {
  currentTime: number;
  animate(animation: Animation): void | (() => void);
}
```

Instead, of passing this to the `Animation` that we start to control the
View Transition keyframes, we instead inverse the control and pass the
`Animation` to this one. It lets any custom implementation drive the
updates. It can do so by updating the time every frame or letting it run
a time based animation (such as momentum scroll).

In this case I added a basic polyfill for `ScrollTimeline` in the
example but we'll need a better one.

.eslintrc.js

@@ -622,6 +622,7 @@ module.exports = {
     ScrollTimeline: 'readonly',
     EventListenerOptionsOrUseCapture: 'readonly',
     FocusOptions: 'readonly',
+    OptionalEffectTiming: 'readonly',
 
     spyOnDev: 'readonly',
     spyOnDevAndProd: 'readonly',

fixtures/view-transition/loader/package.json

@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}

fixtures/view-transition/loader/server.js

@@ -0,0 +1,54 @@
+import babel from '@babel/core';
+
+const babelOptions = {
+  babelrc: false,
+  ignore: [/\/(build|node_modules)\//],
+  plugins: [
+    '@babel/plugin-syntax-import-meta',
+    '@babel/plugin-transform-react-jsx',
+  ],
+};
+
+export async function load(url, context, defaultLoad) {
+  if (url.endsWith('.css')) {
+    return {source: 'export default {}', format: 'module', shortCircuit: true};
+  }
+  const {format} = context;
+  const result = await defaultLoad(url, context, defaultLoad);
+  if (result.format === 'module') {
+    const opt = Object.assign({filename: url}, babelOptions);
+    const newResult = await babel.transformAsync(result.source, opt);
+    if (!newResult) {
+      if (typeof result.source === 'string') {
+        return result;
+      }
+      return {
+        source: Buffer.from(result.source).toString('utf8'),
+        format: 'module',
+      };
+    }
+    return {source: newResult.code, format: 'module'};
+  }
+  return defaultLoad(url, context, defaultLoad);
+}
+
+async function babelTransformSource(source, context, defaultTransformSource) {
+  const {format} = context;
+  if (format === 'module') {
+    const opt = Object.assign({filename: context.url}, babelOptions);
+    const newResult = await babel.transformAsync(source, opt);
+    if (!newResult) {
+      if (typeof source === 'string') {
+        return {source};
+      }
+      return {
+        source: Buffer.from(source).toString('utf8'),
+      };
+    }
+    return {source: newResult.code};
+  }
+  return defaultTransformSource(source, context, defaultTransformSource);
+}
+
+export const transformSource =
+  process.version < 'v16' ? babelTransformSource : undefined;

fixtures/view-transition/package.json

@@ -13,7 +13,8 @@
     "express": "^4.14.0",
     "ignore-styles": "^5.0.1",
     "react": "^19.0.0",
-    "react-dom": "^19.0.0"
+    "react-dom": "^19.0.0",
+    "animation-timelines": "^0.0.4"
   },
   "eslintConfig": {
     "extends": [
@@ -27,8 +28,8 @@
     "prebuild": "cp -r ../../build/oss-experimental/* ./node_modules/ && rm -rf node_modules/.cache;",
     "dev": "concurrently \"npm run dev:server\" \"npm run dev:client\"",
     "dev:client": "BROWSER=none PORT=3001 react-scripts start",
-    "dev:server": "NODE_ENV=development node server",
-    "start": "react-scripts build && NODE_ENV=production node server",
+    "dev:server": "NODE_ENV=development node --experimental-loader ./loader/server.js server",
+    "start": "react-scripts build && NODE_ENV=production node --experimental-loader ./loader/server.js server",
     "build": "react-scripts build",
     "test": "react-scripts test --env=jsdom",
     "eject": "react-scripts eject"

fixtures/view-transition/server/index.js

@@ -20,14 +20,16 @@ if (process.env.NODE_ENV === 'development') {
     for (var key in require.cache) {
       delete require.cache[key];
     }
-    const render = require('./render').default;
+    import('./render.js').then(({default: render}) => {
       render(req.url, res);
     });
+  });
 } else {
-  const render = require('./render').default;
+  import('./render.js').then(({default: render}) => {
     app.get('/', function (req, res) {
       render(req.url, res);
     });
+  });
 }
 
 // Static resources

fixtures/view-transition/server/render.js

@@ -1,7 +1,7 @@
 import React from 'react';
 import {renderToPipeableStream} from 'react-dom/server';
 
-import App from '../src/components/App';
+import App from '../src/components/App.js';
 
 let assets;
 if (process.env.NODE_ENV === 'development') {

fixtures/view-transition/src/components/App.js

@@ -6,8 +6,8 @@ import React, {
   unstable_addTransitionType as addTransitionType,
 } from 'react';
 
-import Chrome from './Chrome';
-import Page from './Page';
+import Chrome from './Chrome.js';
+import Page from './Page.js';
 
 const enableNavigationAPI = typeof navigation === 'object';
 

fixtures/view-transition/src/components/Page.js

@@ -13,12 +13,12 @@ import React, {
 
 import {createPortal} from 'react-dom';
 
-import SwipeRecognizer from './SwipeRecognizer';
+import SwipeRecognizer from './SwipeRecognizer.js';
 
 import './Page.css';
 
 import transitions from './Transitions.module.css';
-import NestedReveal from './NestedReveal';
+import NestedReveal from './NestedReveal.js';
 
 async function sleep(ms) {
   return new Promise(resolve => setTimeout(resolve, ms));

fixtures/view-transition/src/components/SwipeRecognizer.js

@@ -5,6 +5,8 @@ import React, {
   unstable_startGestureTransition as startGestureTransition,
 } from 'react';
 
+import ScrollTimelinePolyfill from 'animation-timelines/scroll-timeline';
+
 // Example of a Component that can recognize swipe gestures using a ScrollTimeline
 // without scrolling its own content. Allowing it to be used as an inert gesture
 // recognizer to drive a View Transition.
@@ -25,14 +27,20 @@ export default function SwipeRecognizer({
     if (activeGesture.current !== null) {
       return;
     }
-    if (typeof ScrollTimeline !== 'function') {
-      return;
-    }
+
+    let scrollTimeline;
+    if (typeof ScrollTimeline === 'function') {
       // eslint-disable-next-line no-undef
-    const scrollTimeline = new ScrollTimeline({
+      scrollTimeline = new ScrollTimeline({
         source: scrollRef.current,
         axis: axis,
       });
+    } else {
+      scrollTimeline = new ScrollTimelinePolyfill({
+        source: scrollRef.current,
+        axis: axis,
+      });
+    }
     activeGesture.current = startGestureTransition(
       scrollTimeline,
       () => {

fixtures/view-transition/src/index.js

@@ -1,7 +1,7 @@
 import React from 'react';
 import {hydrateRoot} from 'react-dom/client';
 
-import App from './components/App';
+import App from './components/App.js';
 
 hydrateRoot(
   document,

fixtures/view-transition/yarn.lock

@@ -2427,6 +2427,11 @@ ajv@^8.0.0, ajv@^8.6.0, ajv@^8.9.0:
     json-schema-traverse "^1.0.0"
     require-from-string "^2.0.2"
 
+animation-timelines@^0.0.4:
+  version "0.0.4"
+  resolved "https://registry.yarnpkg.com/animation-timelines/-/animation-timelines-0.0.4.tgz#7ac4614bae73c4d1ea2ff18d5d87a518793258af"
+  integrity sha512-HwCE3m1nM8ZdLbwDwD1j5ZNKmY+3J2CliXJNIsf3y1Si927SIaWpfxkycTg5nWLJSHgjsYxrmOy2Jbo4JR1e9A==
+
 ansi-escapes@^4.2.1, ansi-escapes@^4.3.1:
   version "4.3.2"
   resolved "https://registry.yarnpkg.com/ansi-escapes/-/ansi-escapes-4.3.2.tgz#6b2291d1db7d98b6521d5f1efa42d0f3a9feb65e"

packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js

@@ -2213,7 +2213,8 @@ function animateGesture(
   keyframes: any,
   targetElement: Element,
   pseudoElement: string,
-  timeline: AnimationTimeline,
+  timeline: GestureTimeline,
+  customTimelineCleanup: Array<() => void>,
   rangeStart: number,
   rangeEnd: number,
   moveFirstFrameIntoViewport: boolean,
@@ -2274,6 +2275,8 @@ function animateGesture(
   }
   // TODO: Reverse the reverse if the original direction is reverse.
   const reverse = rangeStart > rangeEnd;
+  if (timeline instanceof AnimationTimeline) {
+    // Native Timeline
     targetElement.animate(keyframes, {
       pseudoElement: pseudoElement,
       // Set the timeline to the current gesture timeline to drive the updates.
@@ -2292,6 +2295,29 @@ function animateGesture(
       rangeStart: (reverse ? rangeEnd : rangeStart) + '%',
       rangeEnd: (reverse ? rangeStart : rangeEnd) + '%',
     });
+  } else {
+    // Custom Timeline
+    const animation = targetElement.animate(keyframes, {
+      pseudoElement: pseudoElement,
+      // We reset all easing functions to linear so that it feels like you
+      // have direct impact on the transition and to avoid double bouncing
+      // from scroll bouncing.
+      easing: 'linear',
+      // We fill in both direction for overscroll.
+      fill: 'both', // TODO: Should we preserve the fill instead?
+      // We play all gestures in reverse, except if we're in reverse direction
+      // in which case we need to play it in reverse of the reverse.
+      direction: reverse ? 'normal' : 'reverse',
+      // We set the delay and duration to represent the span of the range.
+      delay: reverse ? rangeEnd : rangeStart,
+      duration: reverse ? rangeStart - rangeEnd : rangeEnd - rangeStart,
+    });
+    // Let the custom timeline take control of driving the animation.
+    const cleanup = timeline.animate(animation);
+    if (cleanup) {
+      customTimelineCleanup.push(cleanup);
+    }
+  }
 }
 
 export function startGestureTransition(
@@ -2320,6 +2346,7 @@ export function startGestureTransition(
     });
     // $FlowFixMe[prop-missing]
     ownerDocument.__reactViewTransition = transition;
+    const customTimelineCleanup: Array<() => void> = []; // Cleanup Animations started in a CustomTimeline
     const readyCallback = () => {
       const documentElement: Element = (ownerDocument.documentElement: any);
       // Loop through all View Transition Animations.
@@ -2419,6 +2446,7 @@ export function startGestureTransition(
             effect.target,
             pseudoElement,
             timeline,
+            customTimelineCleanup,
             adjustedRangeStart,
             adjustedRangeEnd,
             isGeneratedGroupAnim,
@@ -2445,6 +2473,7 @@ export function startGestureTransition(
                 effect.target,
                 pseudoElementName,
                 timeline,
+                customTimelineCleanup,
                 rangeStart,
                 rangeEnd,
                 false,
@@ -2494,6 +2523,10 @@ export function startGestureTransition(
     transition.ready.then(readyForAnimations, handleError);
     transition.finished.finally(() => {
       cancelAllViewTransitionAnimations((ownerDocument.documentElement: any));
+      for (let i = 0; i < customTimelineCleanup.length; i++) {
+        const cleanup = customTimelineCleanup[i];
+        cleanup();
+      }
       // $FlowFixMe[prop-missing]
       if (ownerDocument.__reactViewTransition === transition) {
         // $FlowFixMe[prop-missing]
@@ -2597,10 +2630,15 @@ export function createViewTransitionInstance(
   };
 }
 
-export type GestureTimeline = AnimationTimeline; // TODO: More provider types.
+interface CustomTimeline {
+  currentTime: number;
+  animate(animation: Animation): void | (() => void);
+}
 
-export function getCurrentGestureOffset(provider: GestureTimeline): number {
-  const time = provider.currentTime;
+export type GestureTimeline = AnimationTimeline | CustomTimeline;
+
+export function getCurrentGestureOffset(timeline: GestureTimeline): number {
+  const time = timeline.currentTime;
   if (time === null) {
     throw new Error(
       'Cannot start a gesture with a disconnected AnimationTimeline.',