react-use/docs/usePreviousDistinct.md

usePreviousDistinct

Just like usePrevious but it will only update once the value actually changes. This is important when other hooks are involved and you aren't just interested in the previous props version, but want to know the previous distinct value

Usage

import {usePreviousDistinct, useCounter} from 'react-use';

const Demo = () => {
  const [count, { inc: relatedInc }] = useCounter(0);
  const [unrelatedCount, { inc }] = useCounter(0);
  const prevCount = usePreviousDistinct(count);

  return (
    <p>
      Now: {count}, before: {prevCount}
      <button onClick={() => relatedInc()}>Increment</button>
      Unrelated: {unrelatedCount}
      <button onClick={() => inc()}>Increment Unrelated</button>
    </p>
  );
};

You can also provide a way of identifying the value as unique. By default, a strict equals is used.

import {usePreviousDistinct} from 'react-use';

const Demo = () => {
  const [str, setStr] = React.useState("something_lowercase");
  const [unrelatedCount] = React.useState(0);
  const prevStr = usePreviousDistinct(str, (prev, next) => (prev && prev.toUpperCase()) === next.toUpperCase());

  return (
    <p>
      Now: {count}, before: {prevCount}
      Unrelated: {unrelatedCount}
    </p>
  );
};

Reference

const prevState = usePreviousDistinct = <T>(state: T, compare?: (prev: T | undefined, next: T) => boolean): T;