fix vercel#1680 (vercel#1720)

src/utils/cache.ts

@@ -41,9 +41,10 @@ export const initCache = <Data = any>(
     // If there's no global state bound to the provider, create a new one with the
     // new mutate function.
     const EVENT_REVALIDATORS = {}
-    const mutate = internalMutate.bind(UNDEFINED, provider) as ScopedMutator<
-      Data
-    >
+    const mutate = internalMutate.bind(
+      UNDEFINED,
+      provider
+    ) as ScopedMutator<Data>
     let unmount = noop
 
     // Update the state if it's new, or the provider has been extended.
@@ -60,18 +61,30 @@ export const initCache = <Data = any>(
     // This is a new provider, we need to initialize it and setup DOM events
     // listeners for `focus` and `reconnect` actions.
     if (!IS_SERVER) {
+      // When listening to the native events for auto revalidations,
+      // we intentionally put a delay (setTimeout) here to make sure they are
+      // fired after immediate JavaScript executions, which can possibly be
+      // React's state updates.
+      // This avoids some unnecessary revalidations such as
+      // https://github.com/vercel/swr/issues/1680.
       const releaseFocus = opts.initFocus(
-        revalidateAllKeys.bind(
+        setTimeout.bind(
           UNDEFINED,
-          EVENT_REVALIDATORS,
-          revalidateEvents.FOCUS_EVENT
+          revalidateAllKeys.bind(
+            UNDEFINED,
+            EVENT_REVALIDATORS,
+            revalidateEvents.FOCUS_EVENT
+          )
         )
       )
       const releaseReconnect = opts.initReconnect(
-        revalidateAllKeys.bind(
+        setTimeout.bind(
           UNDEFINED,
-          EVENT_REVALIDATORS,
-          revalidateEvents.RECONNECT_EVENT
+          revalidateAllKeys.bind(
+            UNDEFINED,
+            EVENT_REVALIDATORS,
+            revalidateEvents.RECONNECT_EVENT
+          )
         )
       )
       unmount = () => {

src/utils/web-preset.ts

@@ -36,21 +36,21 @@ const isVisible = () => {
   return true
 }
 
-const initFocus = (cb: () => void) => {
+const initFocus = (callback: () => void) => {
   // focus revalidate
-  onDocumentEvent('visibilitychange', cb)
-  onWindowEvent('focus', cb)
+  onDocumentEvent('visibilitychange', callback)
+  onWindowEvent('focus', callback)
   return () => {
-    offDocumentEvent('visibilitychange', cb)
-    offWindowEvent('focus', cb)
+    offDocumentEvent('visibilitychange', callback)
+    offWindowEvent('focus', callback)
   }
 }
 
-const initReconnect = (cb: () => void) => {
+const initReconnect = (callback: () => void) => {
   // revalidate on reconnected
   const onOnline = () => {
     online = true
-    cb()
+    callback()
   }
   // nothing to revalidate, just update the status
   const onOffline = () => {

test/use-swr-cache.test.tsx

@@ -183,6 +183,7 @@ describe('useSWR - cache provider', () => {
     await screen.findByText('0')
     await nextTick()
     await focusOn(window)
+    await nextTick()
     screen.getByText('1')
   })
 
@@ -396,6 +397,7 @@ describe('useSWR - global cache', () => {
     await screen.findByText('0')
     await nextTick()
     await focusOn(window)
+    await nextTick()
     screen.getByText('1')
   })
 

test/use-swr-focus.test.tsx

@@ -220,4 +220,29 @@ describe('useSWR - focus', () => {
     await focusWindow()
     await screen.findByText('data: 1')
   })
+
+  it('should not revalidate on focus when key changes in the same tick', async () => {
+    const fetchLogs = []
+
+    function Page() {
+      const [key, setKey] = useState(() => createKey())
+      useSWR(key, k => fetchLogs.push(k), {
+        revalidateOnFocus: true,
+        dedupingInterval: 0
+      })
+      return <div onClick={() => setKey(createKey())}>change key</div>
+    }
+
+    renderWithConfig(<Page />)
+    await waitForNextTick()
+
+    fireEvent.focus(window)
+    fireEvent.click(screen.getByText('change key'))
+
+    await waitForNextTick()
+
+    // Only fetched twice with the initial and the new keys.
+    expect(fetchLogs.length).toBe(2)
+    expect(fetchLogs[0]).not.toEqual(fetchLogs[1])
+  })
 })