useWindowSize react Code Snippet in 2025

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);

    handleResize();

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

  return windowSize;
};

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

  return (
    <p>
      Window size: ({width} x {height})
    </p>
  );
};

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