state-hooks/dist-src/usePrevious.js

Essential set of React Hooks for convenient state management.

import { useEffect, useRef } from 'react';
/**
 * Tracks previous state of a value.
 *
 * @param value Props, state or any other calculated value.
 * @returns Value from the previous render of the enclosing component.
 *
 * @example
 * function Component() {
 *   const [count, setCount] = useState(0);
 *   const prevCount = usePrevious(count);
 *   // ...
 *   return `Now: ${count}, before: ${prevCount}`;
 * }
 */
export default function usePrevious(value) {
    // Source: https://reactjs.org/docs/hooks-faq.html#how-to-get-the-previous-props-or-state
    const ref = useRef();
    useEffect(() => {
        ref.current = value;
    });
    return ref.current;
}