Description
Describe the bug
After updating to the latest version of Preact (10.8.0) I've noticed bugs occurring that indicate a hook's cleanup is running unexpectedly.
In particular, under certain circumstances, a useEffect(() => { ... }, []) (which I commonly use as a "on mount/unmount" hook) is triggering even when the component isn't being mounted/unmounted
To Reproduce
Here's an example: https://codesandbox.io/s/modest-ritchie-musy7y?file=/index.js
Operative part:
function Foo() {
const [a, setA] = useState(false);
useEffect(() => {
return () => {
alert("This should only happen when component is unmounted?");
};
}, []);
setA(false);
return <button onClick={() => setA(true)}>Hi</button>;
}Steps to reproduce the behavior:
- Go to the codesandbox above
- Click on "hi"
- Alert pops up.
Expected behavior
Unless I've misunderstood hooks behaviour, the cleanup for a useEffect with empty arguments should only ever be called when the component is being unmounted. And since no unmounting is happening in the above example, the alert should never fire.
I've confirmed that this behaviour is fine with Preact up to and including 10.7.3 and only started appearing in 10.8.0