How to detect window size in Next.js SSR using react hook?

You can avoid calling your detection function in ssr by adding this code:

// make sure your function is being called in client side only
if (typeof window !== 'undefined') {
  // detect window screen width function
}

full example from your link:

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(() => {
    // only execute all the code below in client side
    // 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;
}

NB: Updated as Sergey Dubovik comment, we dont need to validate windows since useEffect run in client side