fix issue facebook#19362 + test (facebook#19412)

RobiFerentz · web-flow · commit b55f75d0a538 · 2020-07-24T14:34:16.000-04:00
diff --git a/packages/scheduler/src/Scheduler.js b/packages/scheduler/src/Scheduler.js
@@ -177,7 +177,7 @@ function workLoop(hasTimeRemaining, initialTime) {
       break;
     }
     const callback = currentTask.callback;
-    if (callback !== null) {
+    if (typeof callback === 'function') {
       currentTask.callback = null;
       currentPriorityLevel = currentTask.priorityLevel;
       const didUserCallbackTimeout = currentTask.expirationTime <= currentTime;
diff --git a/packages/scheduler/src/__tests__/Scheduler-test.js b/packages/scheduler/src/__tests__/Scheduler-test.js
@@ -739,5 +739,19 @@ describe('Scheduler', () => {
       // Only A should flush
       expect(Scheduler).toFlushAndYield(['A']);
     });
+
+    it('gracefully handles scheduled tasks that are not a function', () => {
+      scheduleCallback(ImmediatePriority, null);
+      expect(Scheduler).toFlushWithoutYielding();
+
+      scheduleCallback(ImmediatePriority, undefined);
+      expect(Scheduler).toFlushWithoutYielding();
+
+      scheduleCallback(ImmediatePriority, {});
+      expect(Scheduler).toFlushWithoutYielding();
+
+      scheduleCallback(ImmediatePriority, 42);
+      expect(Scheduler).toFlushWithoutYielding();
+    });
   });
 });

Original file line number	Diff line number	Diff line change
`@@ -177,7 +177,7 @@ function workLoop(hasTimeRemaining, initialTime) {`
`177`	`177`	`break;`
`178`	`178`	`}`
`179`	`179`	`const callback = currentTask.callback;`
`180`		`- if (callback !== null) {`
	`180`	`+ if (typeof callback === 'function') {`
`181`	`181`	`currentTask.callback = null;`
`182`	`182`	`currentPriorityLevel = currentTask.priorityLevel;`
`183`	`183`	`const didUserCallbackTimeout = currentTask.expirationTime <= currentTime;`