React, Hooks, State, Effect

Tracks the dimensions of the browser window.

  • Use the useState() hook to initialize a state variable that will hold the window's dimensions. Initialize with both values set to undefined to avoid mismatch between server and client renders.
  • Create a function that uses Window.innerWidth and Window.innerHeight to update the state variable.
  • Use the useEffect() hook to set an appropriate listener for the 'resize' event on mount and clean it up when unmounting.
const useWindowSize = () => {
  const [windowSize, setWindowSize] = React.useState({
    width: undefined,
    height: undefined,

  React.useEffect(() => {
    const handleResize = () =>
      setWindowSize({ width: window.innerWidth, height: window.innerHeight });

    window.addEventListener('resize', handleResize);


    return () => {
      window.removeEventListener('resize', handleResize);
  }, []);

  return windowSize;
const MyApp = () => {
  const { width, height } = useWindowSize();

  return (
      Window size: ({width} x {height})

ReactDOM.render(<MyApp />, document.getElementById('root'));

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