[scheduler] Remove window.postMessage fallback

acdlite · acdlite · commit 8feeed10d8f7 · 2018-11-14T14:44:26.000-08:00
Every browser we can about supports MessageChannel. The ones we don't
care about will fallback to the setTimeout implementation.
diff --git a/packages/react-dom/src/__tests__/ReactDOM-test.js b/packages/react-dom/src/__tests__/ReactDOM-test.js
@@ -450,22 +450,6 @@ describe('ReactDOM', () => {
     }
   });
 
-  it('warns when requestAnimationFrame is not polyfilled', () => {
-    const previousRAF = global.requestAnimationFrame;
-    try {
-      delete global.requestAnimationFrame;
-      jest.resetModules();
-      spyOnDevAndProd(console, 'error');
-      require('react-dom');
-      expect(console.error.calls.count()).toEqual(1);
-      expect(console.error.calls.argsFor(0)[0]).toMatch(
-        "This browser doesn't support requestAnimationFrame.",
-      );
-    } finally {
-      global.requestAnimationFrame = previousRAF;
-    }
-  });
-
   it('reports stacks with re-entrant renderToString() calls on the client', () => {
     function Child2(props) {
       return <span ariaTypo3="no">{props.children}</span>;
diff --git a/packages/scheduler/src/Scheduler.js b/packages/scheduler/src/Scheduler.js
@@ -457,9 +457,8 @@ if (typeof window !== 'undefined' && window._schedMock) {
   // If Scheduler runs in a non-DOM environment, it falls back to a naive
   // implementation using setTimeout.
   typeof window === 'undefined' ||
-  // "addEventListener" might not be available on the window object
-  // if this is a mocked "window" object. So we need to validate that too.
-  typeof window.addEventListener !== 'function'
+  // Check if MessageChannel is supported, too.
+  typeof MessageChannel !== 'function'
 ) {
   var _callback = null;
   var _currentTime = -1;
@@ -533,17 +532,9 @@ if (typeof window !== 'undefined' && window._schedMock) {
   };
 
   // We use the postMessage trick to defer idle work until after the repaint.
-  var port = null;
-  var messageKey =
-    '__reactIdleCallback$' +
-    Math.random()
-      .toString(36)
-      .slice(2);
-  var idleTick = function(event) {
-    if (event.source !== port || event.data !== messageKey) {
-      return;
-    }
-
+  var channel = new MessageChannel();
+  var port = channel.port2;
+  channel.port1.onmessage = function(event) {
     isMessageEventScheduled = false;
 
     var prevScheduledCallback = scheduledHostCallback;
@@ -627,7 +618,7 @@ if (typeof window !== 'undefined' && window._schedMock) {
     frameDeadline = rafTime + activeFrameTime;
     if (!isMessageEventScheduled) {
       isMessageEventScheduled = true;
-      port.postMessage(messageKey, '*');
+      port.postMessage('*');
     }
   };
 
@@ -636,7 +627,7 @@ if (typeof window !== 'undefined' && window._schedMock) {
     timeoutTime = absoluteTimeout;
     if (isFlushingHostCallback || absoluteTimeout < 0) {
       // Don't wait for the next frame. Continue working ASAP, in a new event.
-      port.postMessage(messageKey, '*');
+      port.postMessage('*');
     } else if (!isAnimationFrameScheduled) {
       // If rAF didn't already schedule one, we need to schedule a frame.
       // TODO: If this rAF doesn't materialize because the browser throttles, we
@@ -647,19 +638,6 @@ if (typeof window !== 'undefined' && window._schedMock) {
     }
   };
 
-  if (typeof MessageChannel === 'function') {
-    // Use a MessageChannel, if support exists
-    var channel = new MessageChannel();
-    channel.port1.onmessage = idleTick;
-    port = channel.port2;
-  } else {
-    // Otherwise post a message to the window. This isn't ideal because message
-    // handlers will fire on every frame until the queue is empty, including
-    // some browser extensions.
-    window.addEventListener('message', idleTick, false);
-    port = window;
-  }
-
   cancelHostCallback = function() {
     scheduledHostCallback = null;
     isMessageEventScheduled = false;
diff --git a/packages/scheduler/src/__tests__/SchedulerDOM-test.js b/packages/scheduler/src/__tests__/SchedulerDOM-test.js
@@ -83,7 +83,7 @@ describe('SchedulerDOM', () => {
       this.port1 = port1;
       this.port2 = port2;
     };
-    postMessageCallback = event => port1.onmessage(event);
+    postMessageCallback = () => port1.onmessage();
     global.Date.now = function() {
       return currentTime;
     };
diff --git a/packages/shared/__tests__/ReactDOMFrameScheduling-test.js b/packages/shared/__tests__/ReactDOMFrameScheduling-test.js
@@ -12,8 +12,15 @@
 describe('ReactDOMFrameScheduling', () => {
   it('warns when requestAnimationFrame is not polyfilled in the browser', () => {
     const previousRAF = global.requestAnimationFrame;
+    const previousMessageChannel = global.MessageChannel;
     try {
-      global.requestAnimationFrame = undefined;
+      delete global.requestAnimationFrame;
+      global.MessageChannel = function MessageChannel() {
+        return {
+          port1: {},
+          port2: {},
+        };
+      };
       jest.resetModules();
       spyOnDevAndProd(console, 'error');
       require('react-dom');
@@ -22,6 +29,7 @@ describe('ReactDOMFrameScheduling', () => {
         "This browser doesn't support requestAnimationFrame.",
       );
     } finally {
+      global.MessageChannel = previousMessageChannel;
       global.requestAnimationFrame = previousRAF;
     }
   });
