React Hook recipe from https://usehooks.com. Demo: https://codesandbox.io/s/jj61r2w6z5

use-window-size.js

import { useState, useEffect } from 'react';

// Usage
function App() {
  const size = useWindowSize();

  return (
    <div>
      {size.width}px / {size.height}px
    </div>
  );
}

// Hook
function useWindowSize() {
  // Initialize state with undefined width/height so server and client renders match
  // Learn more here: https://joshwcomeau.com/react/the-perils-of-rehydration/
  const [windowSize, setWindowSize] = useState({
    width: undefined,
    height: undefined,
  });

  useEffect(() => {
    // Handler to call on window resize
    function handleResize() {
      // Set window width/height to state
      setWindowSize({
        width: window.innerWidth,
        height: window.innerHeight,
      });
    }
    
    // Add event listener
    window.addEventListener("resize", handleResize);
    
    // Call handler right away so state gets updated with initial window size
    handleResize();
    
    // Remove event listener on cleanup
    return () => window.removeEventListener("resize", handleResize);
  }, []); // Empty array ensures that effect is only run on mount

  return windowSize;
}

When I use this hook twice, it adds Event Listener to window twice. Should this be adding only once and Event caching needed ?

react_devtools_backend.js:6 ./src/utils/useWindowSize.js
  Line 27:6:  React Hook useEffect has missing dependencies: 'getSize' and 'isClient'. Either include them or remove the dependency array  react-hooks/exhaustive-deps

Hello! 👋🏻

This code has an issue with server rendering. I ran in to a similar issue here: gatsbyjs/gatsby#14601

The underlying issue is in getSize

return {
  width: isClient ? window.innerWidth : undefined,
  height: isClient ? window.innerHeight : undefined
};

The problem is that the server render value of windowSize and the first client render won't match. (eg, width on the server will be undefined, client will be window.innerWidth). This confuses React and you will see incorrect values on first load, as described in the github issue above and demonstrated here on a large screen: http://mikelambert.me/gatsby-bug/

To fix this, I modified the hook to always initialize the values to undefined (so the server render and first client render match) and to update the values after the first render on the client.

export default function useWindowSize() {
  // initialize to undefined so the server render and first client render match
  // https://github.com/gatsbyjs/gatsby/issues/14601 
  const [windowSize, setWindowSize] = useState({
    width: undefined,
    height: undefined,
  });

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

    window.addEventListener("resize", handleResize);
    handleResize();

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

  return windowSize;
}

@lax4mike thanks for pointing out the SSR issue! I've updated this gist and the post.

change the useEffect to useLayoutEffect because you see a flicker before it's set in some cases. useLayoutEffect is definitely the way to go here. Here an example where a div is centered based on the body, if you change it to a normal useEffect you will see it flicker. https://codesandbox.io/s/still-wave-q0pk7

Long time has passed , why haven't this been updated with debounce or throttle ?