BFE.devAI解答 - React 代码题
14. implement useIsMounted()

Here's an implementation of useIsMounted() using the useState hook:

import { useState, useEffect } from 'react';

function useIsMounted() {
  const [isMounted, setIsMounted] = useState(false);

  useEffect(() => {
    setIsMounted(true);
    // The useEffect function returned here is called when the component is unmounting
    return () => setIsMounted(false);
  }, []);

  return isMounted;
}

The useState hook initializes a isMounted state variable to false.

The useEffect hook is called with an empty array as the second argument, which means it will only be called once, when the component mounts.

The effect function sets the isMounted state variable to true.

We also return a cleanup function, which sets the isMounted state variable to false when the component unmounts.

The hook returns the isMounted state variable, which is true when the component is mounted and false otherwise.