1

During reconciliation react compares trees and gets differences. Does it make sense to decrease those differences by using memoization hooks when components are not memoized?

Example:

// Does useCallback make sense here?
const onPress = useCallback(() => console.log('Press!'), []);

return (
  <Pressable onPress={onPress}/> // Pressable is neither a memoized FC nor a PureComponent
)

EDIT: Would be nice to receive some numbers, e.g. performance decrease/improvement in ms, and especially for react native.

Alexander Danilov
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3 Answers3

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So react automatically have a memoize system that checks the diffs of all components props when rendering, regardless of your component being memorized. With this system react checks on only the primitive types (Number, String, Boolean, etc).

But if you pass a function as props and want react to memoize that function calls then the useCallback becomes useful.

react useCallback useCallback

Ritchid Amoah
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No. React is way too fast in general. useCallback and useMemo are supposed to be used only when required.

Note: "Premature optimization is the root of all evil" ref

useCallback and useMemo come with their own overheads. Check this, Kent C Dodds goes in more depth about this.

Think about it this way:

When you scroll a webpage, numerous re-renders keep happening. Even during certain animations there are lot of re-renders but we don't face performance issues due to the speed of browser.

Just to cover extreme cases I'd also suggest you a read of layout thrashing and debounce input handlers

Shravan Dhar
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  • Unfortunately, there are no numbers in that article : / Also, when I scroll web page there could be lots of lags, depends on the web site. – Alexander Danilov Jun 30 '21 at 10:39
0

I don't think so. This is the example in the React.org site.

const memoizedCallback = useCallback(
  () => {
    doSomething(a, b);
  },
  [a, b],
);

Here [a, b] is a dependency list. This means callback is called automatically when a or b has changed. It seems to be not called like yours. You passed no dependencies and callback will not be called. I think you can change in this way if you wanna use callback.

const [pressed, setPressed] = useState(false)
useCallback(() => console.log('Press'), [pressed])

return (
    <Pressable onPress={() => setPressed (pressed => !pressed) } />
)
Chuck
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