Read window.rAF later to allow fake timers to work correctly

packages/toolkit/src/autoBatchEnhancer.ts

@@ -15,13 +15,6 @@ const createQueueWithTimer = (timeout: number) => {
   }
 }
 
-// requestAnimationFrame won't exist in SSR environments.
-// Fall back to a vague approximation just to keep from erroring.
-const rAF =
-  typeof window !== 'undefined' && window.requestAnimationFrame
-    ? window.requestAnimationFrame
-    : createQueueWithTimer(10)
-
 export type AutoBatchOptions =
   | { type: 'tick' }
   | { type: 'timer'; timeout: number }
@@ -66,7 +59,10 @@ export const autoBatchEnhancer =
       options.type === 'tick'
         ? queueMicrotask
         : options.type === 'raf'
-          ? rAF
+          ? // requestAnimationFrame won't exist in SSR environments. Fall back to a vague approximation just to keep from erroring.
+            typeof window !== 'undefined' && window.requestAnimationFrame
+            ? window.requestAnimationFrame
+            : createQueueWithTimer(10)
           : options.type === 'callback'
             ? options.queueNotification
             : createQueueWithTimer(options.timeout)

packages/toolkit/src/tests/autoBatchEnhancer.test.ts

@@ -125,3 +125,84 @@ describe.each(cases)('autoBatchEnhancer: %j', (autoBatchOptions) => {
     expect(subscriptionNotifications).toBe(3)
   })
 })
+
+describe.each(cases)(
+  'autoBatchEnhancer with fake timers: %j',
+  (autoBatchOptions) => {
+    beforeAll(() => {
+      vitest.useFakeTimers({
+        toFake: ['setTimeout', 'queueMicrotask', 'requestAnimationFrame'],
+      })
+    })
+    afterAll(() => {
+      vitest.useRealTimers()
+    })
+    beforeEach(() => {
+      subscriptionNotifications = 0
+      store = makeStore(autoBatchOptions)
+
+      store.subscribe(() => {
+        subscriptionNotifications++
+      })
+    })
+    test('Does not alter normal subscription notification behavior', () => {
+      store.dispatch(decrementUnbatched())
+      expect(subscriptionNotifications).toBe(1)
+      store.dispatch(decrementUnbatched())
+      expect(subscriptionNotifications).toBe(2)
+      store.dispatch(decrementUnbatched())
+      expect(subscriptionNotifications).toBe(3)
+      store.dispatch(decrementUnbatched())
+
+      vitest.runAllTimers()
+
+      expect(subscriptionNotifications).toBe(4)
+    })
+
+    test('Only notifies once if several batched actions are dispatched in a row', () => {
+      store.dispatch(incrementBatched())
+      expect(subscriptionNotifications).toBe(0)
+      store.dispatch(incrementBatched())
+      expect(subscriptionNotifications).toBe(0)
+      store.dispatch(incrementBatched())
+      expect(subscriptionNotifications).toBe(0)
+      store.dispatch(incrementBatched())
+
+      vitest.runAllTimers()
+
+      expect(subscriptionNotifications).toBe(1)
+    })
+
+    test('Notifies immediately if a non-batched action is dispatched', () => {
+      store.dispatch(incrementBatched())
+      expect(subscriptionNotifications).toBe(0)
+      store.dispatch(incrementBatched())
+      expect(subscriptionNotifications).toBe(0)
+      store.dispatch(decrementUnbatched())
+      expect(subscriptionNotifications).toBe(1)
+      store.dispatch(incrementBatched())
+
+      vitest.runAllTimers()
+
+      expect(subscriptionNotifications).toBe(2)
+    })
+
+    test('Does not notify at end of tick if last action was normal priority', () => {
+      store.dispatch(incrementBatched())
+      expect(subscriptionNotifications).toBe(0)
+      store.dispatch(incrementBatched())
+      expect(subscriptionNotifications).toBe(0)
+      store.dispatch(decrementUnbatched())
+      expect(subscriptionNotifications).toBe(1)
+      store.dispatch(incrementBatched())
+      store.dispatch(decrementUnbatched())
+      expect(subscriptionNotifications).toBe(2)
+      store.dispatch(decrementUnbatched())
+      expect(subscriptionNotifications).toBe(3)
+
+      vitest.runAllTimers()
+
+      expect(subscriptionNotifications).toBe(3)
+    })
+  },
+)