CODEWITHSUNDEEP
javascriptreactjsreact-hooks
agconti
agconti

Reputation: 18093

`useState`, only update component when values in object change

Problem

useState always triggers an update even when the data's values haven't changed.

Here's a working demo of the problem: demo

Background

I'm using the useState hook to update an object and I'm trying to get it to only update when the values in that object change. Because React uses the Object.is comparison algorithm to determine when it should update; objects with equivalent values still cause the component to re-render because they're different objects.

Ex. This component will always re-render even though the value of the payload stays as { foo: 'bar' }

const UseStateWithNewObject = () => {
  const [payload, setPayload] = useState({});
  useEffect(
    () => {
      setInterval(() => {
        setPayload({ foo: 'bar' });
      }, 500);
    },
    [setPayload]
  );

  renderCountNewObject += 1;
  return <h3>A new object, even with the same values, will always cause a render: {renderCountNewObject}</h3>;
};

Question

Is there away that I can implement something like shouldComponentUpdate with hooks to tell react to only re-render my component when the data changes?

Upvotes: 23

Views: 32400

Answers (5)

klugjo
klugjo

Reputation: 20885

If I understand well, you are trying to only call setState whenever the new value for the state has changed, thus preventing unnecessary rerenders when it has NOT changed.

If that is the case you can take advantage of the callback form of useState

const [state, setState] = useState({});
setState(prevState => {
  // here check for equality and return prevState if the same

  // If the same
  return prevState; // -> NO RERENDER !

  // If different
  return {...prevState, ...updatedValues}; // Rerender
});

Here is a custom hook (in TypeScript) that does that for you automatically. It uses isEqual from lodash. But feel free to replace it with whatever equality function you see fit.

import { isEqual } from 'lodash';
import { useState } from 'react';

const useMemoizedState = <T>(initialValue: T): [T, (val: T) => void] => {
  const [state, _setState] = useState<T>(initialValue);

  const setState = (newState: T) => {
    _setState((prev) => {
      if (!isEqual(newState, prev)) {
        return newState;
      } else {
        return prev;
      }
    });
  };

  return [state, setState];
};

export default useMemoizedState;

Usage:

const [value, setValue] = useMemoizedState({ [...] });

Upvotes: 20

Travis James
Travis James

Reputation: 1939

I think we would need to see a better real life example of what you are tying to do, but from what you have shared I think the logic would need to move upstream to a point before the state gets set.

For example, you could manually compare the incoming values in a useEffect before you update state, because this is basically what you are asking if React can do for you.

There is a library use-deep-compare-effect https://github.com/kentcdodds/use-deep-compare-effect that may be of use to you in this case, taking care of a lot of the manual effort involved, but even then, this solution assumes the developer is going to manually decide (based on incoming props, etc) if the state should be updated.

So for example:

const obj = {foo: 'bar'}
const [state, setState] = useState(obj)

useEffect(() => {
   // manually deep compare here before updating state
   if(obj.foo === state.foo) return
   setState(obj)
},[obj])

EDIT: Example using useRef if you don't use the value directly and don't need the component to update based on it:

const obj = {foo: 'bar'}
const [state, setState] = useState(obj)

const { current: payload } = useRef(obj)

useEffect(() => {
    // always update the ref with the current value - won't affect renders
    payload = obj

    // Now manually deep compare here and only update the state if 
    //needed/you want a re render
    if(obj.foo === state.foo) return
    setState(obj)
},[obj])

Upvotes: 4

Dennis Vash
Dennis Vash

Reputation: 53884

Is there away that I can implement something like shouldComponentUpdate with hooks to tell react to only re-render my component when the data changes?

Commonly, for state change you compare with previous value before rendering with functional useState or a reference using useRef:

// functional useState
useEffect(() => {
  setInterval(() => {
    const curr = { foo: 'bar' };
    setPayload(prev => (isEqual(prev, curr) ? prev : curr));
  }, 500);
}, [setPayload]);

// with ref
const prev = useRef();
useEffect(() => {
  setInterval(() => {
    const curr = { foo: 'bar' };
    if (!isEqual(prev.current, curr)) {
      setPayload(curr);
    }
  }, 500);
}, [setPayload]);

useEffect(() => {
  prev.current = payload;
}, [payload]);

For completeness, "re-render my component when the data changes?" may be referred to props too, so in this case, you should use React.memo.

If your function component renders the same result given the same props, you can wrap it in a call to React.memo for a performance boost in some cases by memoizing the result. This means that React will skip rendering the component, and reuse the last rendered result.

Edit affectionate-hellman-ujtbv

Upvotes: 1

Brandon
Brandon

Reputation: 39192

The generic solution to this that does not involve adding logic to your effects, is to split your components into:

  • uncontrolled container with state that renders...
  • dumb controlled stateless component that has been memoized with React.memo

Your dumb component can be pure (as if it had shouldComponentUpdate implemented and your smart state handling component can be "dumb" and not worry about updating state to the same value.

Example:

Before

export default function Foo() {
  const [state, setState] = useState({ foo: "1" })
  const handler = useCallback(newValue => setState({ foo: newValue }))

  return (
    <div>
      <SomeWidget onEvent={handler} />
      Value: {{ state.foo }}
    </div>
  )

After

const FooChild = React.memo(({foo, handler}) => {
  return (
    <div>
      <SomeWidget onEvent={handler} />
      Value: {{ state.foo }}
    </div>
  )
})

export default function Foo() {
  const [state, setState] = useState({ foo: "1" })
  const handler = useCallback(newValue => setState({ foo: newValue }))

  return <FooChild handler={handler} foo={state.foo} />
}

This gives you the separation of logic you are looking for.

Upvotes: 0

meneroush
meneroush

Reputation: 69

You can use memoized components, they will re-render only on prop changes.

const comparatorFunc = (prev, next) => {
  return prev.foo === next.foo
}

const MemoizedComponent = React.memo(({payload}) => {
    return (<div>{JSON.stringify(payload)}</div>)
}, comparatorFunc);

Upvotes: -2

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