[Hooks] Alternative useCallback implementation

[edkalina]

According to this page useCallback(fn, inputs) is equivalent to useMemo(() => fn, inputs)

I suggest another one (implemented with current hooks):

function useHandler(handler) {
 const holder = useRef();
 holder.current = handler;

 // TODO: avoid useMemo?
 return useMemo(
 () =>
 function(...args) {
 return holder.current.apply(this, args);
 },
 []
 );
}

It has advantages:

• no need to specify inputs, latest instance of handler will be called
• result of useHandler is constant for all rerenders

[gaearon]

Yeah, we've considered this. It's not clear however what pitfalls this would have in concurrent mode. The particular implementation you propose would definitely have issues (because it mutates during rendering). The one using an effect (like in our FAQ) would be a bit safer but isn't generic purpose (it requires the tree to commit first) and might also have pitfalls.

We have another idea for how to solve this. I described it briefly in react/react#14099 and might add more info there later. Please participate in that issue if you're interested. Thanks!

[ypresto]

For someone searching for what is "async safe" or "mutation of ref during rendering" problem, it is described here:
react/react#14099 (comment)

In concurrent mode (not yet released), it would "remember" the last rendered version, which isn't great if we render different work-in-progress priorities. So it's not "async safe".

[LiuJi-Jim]

Looks like ahooks/usePersistFn

[duj26089]

看起来像ahooks/usePersistFn

大佬也研究react么

[gaearon]

We've submitted a proposal to solve this that's largely similar (but works a bit differently). Would appreciate your input.

#220