React — Custom Hooks

Custom Hooks are JavaScript functions that start with use and let you reuse logic across components. They follow the same rules as built-in hooks.

import { useState, useEffect } from 'react';

function useWindowWidth() {
  const [width, setWidth] = useState(window.innerWidth);

  useEffect(() => {
    const handleResize = () => setWidth(window.innerWidth);
    window.addEventListener('resize', handleResize);
    return () => window.removeEventListener('resize', handleResize);
  }, []);

  return width;
}

function App() {
  const width = useWindowWidth();
  return <h1>Window width: {width}px</h1>;
}