useSSR react Code Snippet in 2025

Checks if the code is running on the browser or the server.

• Create a custom hook that returns an appropriate object.
• Use typeof window, window.document and Document.createElement() to check if the code is running on the browser.
• Use the useState() hook to define the inBrowser state variable.
• Use the useEffect() hook to update the inBrowser state variable and clean up at the end.
• Use the useMemo() hook to memoize the return values of the custom hook.

const isDOMavailable = !!(
  typeof window !== 'undefined' &&
  window.document &&
  window.document.createElement
);

const useSSR = () => {
  const [inBrowser, setInBrowser] = React.useState(isDOMavailable);

  React.useEffect(() => {
    setInBrowser(isDOMavailable);
    return () => {
      setInBrowser(false);
    };
  }, []);

  const useSSRObject = React.useMemo(
    () => ({
      isBrowser: inBrowser,
      isServer: !inBrowser,
      canUseWorkers: typeof Worker !== 'undefined',
      canUseEventListeners: inBrowser && !!window.addEventListener,
      canUseViewport: inBrowser && !!window.screen
    }),
    [inBrowser]
  );

  return React.useMemo(
    () => Object.assign(Object.values(useSSRObject), useSSRObject),
    [inBrowser]
  );
};

const SSRChecker = props => {
  let { isBrowser, isServer } = useSSR();

  return <p>{isBrowser ? 'Running on browser' : 'Running on server'}</p>;
};

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