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[useEvent] Non-stable function identity #25473

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merged 5 commits into from
Oct 19, 2022
Merged

[useEvent] Non-stable function identity #25473

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32a6646
[useEvent] Non-stable function identity
poteto Oct 12, 2022
b69bb5d
Test: Events should see latest bindings
acdlite Oct 18, 2022
96ed5e0
Fix failing test
poteto Oct 18, 2022
ef85a49
Don't queue a commit effect on mount
poteto Oct 19, 2022
c8ab997
Inline event function wrapping
poteto Oct 19, 2022
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15 changes: 11 additions & 4 deletions packages/react-reconciler/src/ReactFiberHooks.new.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1928,10 +1928,9 @@ function useEventImpl<Args, Return, F: (...Array<Args>) => Return>(
}
}

function mountEvent<Args, Return, F: (...Array<Args>) => Return>(
function wrapEventFunction<Args, Return, F: (...Array<Args>) => Return>(
callback: F,
): EventFunctionWrapper<Args, Return, F> {
const hook = mountWorkInProgressHook();
const eventFn: EventFunctionWrapper<Args, Return, F> = function eventFn() {
if (isInvalidExecutionContextForEventFunction()) {
throw new Error(
Expand All @@ -1942,9 +1941,16 @@ function mountEvent<Args, Return, F: (...Array<Args>) => Return>(
return eventFn._impl.apply(undefined, arguments);
};
eventFn._impl = callback;
return eventFn;
}

useEventImpl(eventFn, callback);
function mountEvent<Args, Return, F: (...Array<Args>) => Return>(
callback: F,
): EventFunctionWrapper<Args, Return, F> {
const hook = mountWorkInProgressHook();
const eventFn = wrapEventFunction(callback);
hook.memoizedState = eventFn;
useEventImpl(eventFn, callback);
return eventFn;
}

Expand All @@ -1954,7 +1960,8 @@ function updateEvent<Args, Return, F: (...Array<Args>) => Return>(
const hook = updateWorkInProgressHook();
const eventFn = hook.memoizedState;
useEventImpl(eventFn, callback);
return eventFn;
// Always return a new function
return wrapEventFunction(callback);
}

function mountInsertionEffect(
Expand Down
15 changes: 11 additions & 4 deletions packages/react-reconciler/src/ReactFiberHooks.old.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1928,10 +1928,9 @@ function useEventImpl<Args, Return, F: (...Array<Args>) => Return>(
}
}

function mountEvent<Args, Return, F: (...Array<Args>) => Return>(
function wrapEventFunction<Args, Return, F: (...Array<Args>) => Return>(
callback: F,
): EventFunctionWrapper<Args, Return, F> {
const hook = mountWorkInProgressHook();
const eventFn: EventFunctionWrapper<Args, Return, F> = function eventFn() {
if (isInvalidExecutionContextForEventFunction()) {
throw new Error(
Expand All @@ -1942,9 +1941,16 @@ function mountEvent<Args, Return, F: (...Array<Args>) => Return>(
return eventFn._impl.apply(undefined, arguments);
};
eventFn._impl = callback;
return eventFn;
}

useEventImpl(eventFn, callback);
function mountEvent<Args, Return, F: (...Array<Args>) => Return>(
callback: F,
): EventFunctionWrapper<Args, Return, F> {
const hook = mountWorkInProgressHook();
const eventFn = wrapEventFunction(callback);
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Nit: Now that we don't reuse the eventFn anymore, there's not any advantage to using it in place of a ref-style mutable object. So I would change this back to something like {impl: eventFn} to avoid confusion.

Also I'm noticing now that during initial render, you don't need to schedule a commit effect. It's already initialized to the correct implementation.

hook.memoizedState = eventFn;
useEventImpl(eventFn, callback);
return eventFn;
}

Expand All @@ -1954,7 +1960,8 @@ function updateEvent<Args, Return, F: (...Array<Args>) => Return>(
const hook = updateWorkInProgressHook();
const eventFn = hook.memoizedState;
useEventImpl(eventFn, callback);
return eventFn;
// Always return a new function
return wrapEventFunction(callback);
}

function mountInsertionEffect(
Expand Down
93 changes: 91 additions & 2 deletions packages/react-reconciler/src/__tests__/useEvent-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -557,6 +557,95 @@ describe('useEvent', () => {
expect(Scheduler).toHaveYielded(['Effect value: 2', 'Event value: 2']);
});

// @gate enableUseEventHook
it("doesn't provide a stable identity", () => {
function Counter({shouldRender, value}) {
const onClick = useEvent(() => {
Scheduler.unstable_yieldValue(
'onClick, shouldRender=' + shouldRender + ', value=' + value,
);
});

// onClick doesn't have a stable function identity so this effect will fire on every render.
// In a real app useEvent functions should *not* be passed as a dependency, this is for
// testing purposes only.
useEffect(() => {
onClick();
}, [onClick]);
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useEffect(() => {
onClick();
}, [shouldRender]);

return <></>;
}

ReactNoop.render(<Counter shouldRender={true} value={0} />);
expect(Scheduler).toFlushAndYield([
'onClick, shouldRender=true, value=0',
'onClick, shouldRender=true, value=0',
]);

ReactNoop.render(<Counter shouldRender={true} value={1} />);
expect(Scheduler).toFlushAndYield(['onClick, shouldRender=true, value=1']);

ReactNoop.render(<Counter shouldRender={false} value={2} />);
expect(Scheduler).toFlushAndYield([
'onClick, shouldRender=false, value=2',
'onClick, shouldRender=false, value=2',
]);
});

// @gate enableUseEventHook
it('event handlers always see the latest committed value', async () => {
let committedEventHandler = null;

function App({value}) {
const event = useEvent(() => {
return 'Value seen by useEvent: ' + value;
});

// Set up an effect that registers the event handler with an external
// event system (e.g. addEventListener).
useEffect(
() => {
// Log when the effect fires. In the test below, we'll assert that this
// only happens during initial render, not during updates.
Scheduler.unstable_yieldValue('Commit new event handler');
committedEventHandler = event;
return () => {
committedEventHandler = null;
};
},
// Note that we've intentionally omitted the event from the dependency
// array. But it will still be able to see the latest `value`. This is the
// key feature of useEvent that makes it different from a regular closure.
[],
);
return 'Latest rendered value ' + value;
}

// Initial render
const root = ReactNoop.createRoot();
await act(async () => {
root.render(<App value={1} />);
});
expect(Scheduler).toHaveYielded(['Commit new event handler']);
expect(root).toMatchRenderedOutput('Latest rendered value 1');
expect(committedEventHandler()).toBe('Value seen by useEvent: 1');

// Update
await act(async () => {
root.render(<App value={2} />);
});
// No new event handler should be committed, because it was omitted from
// the dependency array.
expect(Scheduler).toHaveYielded([]);
// But the event handler should still be able to see the latest value.
expect(root).toMatchRenderedOutput('Latest rendered value 2');
expect(committedEventHandler()).toBe('Value seen by useEvent: 2');
});

// @gate enableUseEventHook
it('integration: implements docs chat room example', () => {
function createConnection() {
Expand Down Expand Up @@ -597,7 +686,7 @@ describe('useEvent', () => {
});
connection.connect();
return () => connection.disconnect();
}, [roomId, onConnected]);
}, [roomId]);

return <Text text={`Welcome to the ${roomId} room!`} />;
}
Expand Down Expand Up @@ -676,7 +765,7 @@ describe('useEvent', () => {

const onVisit = useEvent(visitedUrl => {
Scheduler.unstable_yieldValue(
'url: ' + url + ', numberOfItems: ' + numberOfItems,
'url: ' + visitedUrl + ', numberOfItems: ' + numberOfItems,
);
});

Expand Down