[Fizz] useEvent

Author: gaearon

packages/react-dom/src/__tests__/ReactDOMFizzServer-test.js

@@ -5545,4 +5545,105 @@ describe('ReactDOMFizzServer', () => {
       expect(getVisibleChildren(container)).toEqual('Hi');
     });
   });
+
+  describe('useEvent', () => {
+    // @gate enableUseEventHook
+    it('can server render a component with useEvent', async () => {
+      const ref = React.createRef();
+      function App() {
+        const [count, setCount] = React.useState(0);
+        const onClick = React.experimental_useEvent(() => {
+          setCount(c => c + 1);
+        });
+        return (
+          <button ref={ref} onClick={() => onClick()}>
+            {count}
+          </button>
+        );
+      }
+      await act(async () => {
+        const {pipe} = ReactDOMFizzServer.renderToPipeableStream(<App />);
+        pipe(writable);
+      });
+      expect(getVisibleChildren(container)).toEqual(<button>0</button>);
+
+      ReactDOMClient.hydrateRoot(container, <App />);
+      expect(Scheduler).toFlushAndYield([]);
+      expect(getVisibleChildren(container)).toEqual(<button>0</button>);
+
+      ref.current.dispatchEvent(
+        new window.MouseEvent('click', {bubbles: true}),
+      );
+      await jest.runAllTimers();
+      expect(getVisibleChildren(container)).toEqual(<button>1</button>);
+    });
+
+    // @gate enableUseEventHook
+    it('throws if useEvent is called during a server render', async () => {
+      const logs = [];
+      function App() {
+        const onRender = React.experimental_useEvent(() => {
+          logs.push('rendered');
+        });
+        onRender();
+        return <p>Hello</p>;
+      }
+
+      const reportedServerErrors = [];
+      let caughtError;
+      try {
+        await act(async () => {
+          const {pipe} = ReactDOMFizzServer.renderToPipeableStream(<App />, {
+            onError(e) {
+              reportedServerErrors.push(e);
+            },
+          });
+          pipe(writable);
+        });
+      } catch (err) {
+        caughtError = err;
+      }
+      expect(logs).toEqual([]);
+      expect(caughtError.message).toContain(
+        'Cannot call a function returned by useEvent',
+      );
+      expect(reportedServerErrors).toEqual([caughtError]);
+    });
+
+    // @gate enableUseEventHook
+    it('does not guarantee useEvent return values during server rendering are distinct', async () => {
+      function App() {
+        const onClick1 = React.experimental_useEvent(() => {});
+        const onClick2 = React.experimental_useEvent(() => {});
+        if (onClick1 === onClick2) {
+          return <div />;
+        } else {
+          return <span />;
+        }
+      }
+      await act(async () => {
+        const {pipe} = ReactDOMFizzServer.renderToPipeableStream(<App />);
+        pipe(writable);
+      });
+      expect(getVisibleChildren(container)).toEqual(<div />);
+
+      const errors = [];
+      ReactDOMClient.hydrateRoot(container, <App />, {
+        onRecoverableError(error) {
+          errors.push(error);
+        },
+      });
+      expect(() => {
+        expect(Scheduler).toFlushAndYield([]);
+      }).toErrorDev(
+        [
+          'Expected server HTML to contain a matching <span> in <div>',
+          'An error occurred during hydration',
+        ],
+        {withoutStack: 1},
+      );
+      expect(errors.length).toEqual(2);
+      expect(getVisibleChildren(container)).toEqual(<span />);
+    });
+  });
 });

packages/react-server/src/ReactFizzHooks.js

@@ -36,6 +36,7 @@ import {makeId} from './ReactServerFormatConfig';
 import {
   enableCache,
   enableUseHook,
+  enableUseEventHook,
   enableUseMemoCacheHook,
 } from 'shared/ReactFeatureFlags';
 import is from 'shared/objectIs';
@@ -502,6 +503,16 @@ export function useCallback<T>(
   return useMemo(() => callback, deps);
 }
 
+function throwOnUseEventCall() {
+  throw new Error(
+    'Cannot call a function returned by useEvent during server rendering.',
+  );
+}
+
+export function useEvent<T>(callback: () => T): () => T {
+  return throwOnUseEventCall;
+}
+
 // TODO Decide on how to implement this hook for server rendering.
 // If a mutation occurs during render, consider triggering a Suspense boundary
 // and falling back to client rendering.
@@ -675,6 +686,9 @@ if (enableCache) {
   Dispatcher.getCacheForType = getCacheForType;
   Dispatcher.useCacheRefresh = useCacheRefresh;
 }
+if (enableUseEventHook) {
+  Dispatcher.useEvent = useEvent;
+}
 if (enableUseMemoCacheHook) {
   Dispatcher.useMemoCache = useMemoCache;
 }

scripts/error-codes/codes.json

@@ -426,5 +426,6 @@
   "438": "An unsupported type was passed to use(): %s",
   "439": "We didn't expect to see a forward reference. This is a bug in the React Server.",
   "440": "An event from useEvent was called during render.",
-  "441": "An error occurred in the Server Components render. The specific message is omitted in production builds to avoid leaking sensitive details. A digest property is included on this error instance which may provide additional details about the nature of the error."
-}
+  "441": "An error occurred in the Server Components render. The specific message is omitted in production builds to avoid leaking sensitive details. A digest property is included on this error instance which may provide additional details about the nature of the error.",
+  "442": "Cannot call a function returned by useEvent during server rendering."
+}