Welcome to Blogvent, day 5!

Chances are if you’ve written any CSS before, you’ve written media queries. And honestly, media queries overall are solid! But, they were made for an earlier time in the browser. They were not designed for some of the rendering logic that we have on the frontend now.

You can still use media queries, of course, and should, but there are some cases where JavaScript will be a smarter option. For example, what if you’re on your phone, and browsing a website, and there is a sidebar or element that is hidden by CSS, that is making network requests? For the user, that is a waste of resources!

There has to be a better way. And there is!

Media queries… in JavaScript!

So, to solve this problem, what you need to do here is conditionally render things based on the browser size, rather than render something and hide it with CSS.

If you’ll recall in yesterday’s Blogvent post, you can use React’s useEffect to access the window object in the browser. That window object has a function called matchMedia that returns a boolean based on if the window matches a certain media query passed in!

So, if we combine these with a little bit of state, you can make a custom hook that you can use to conditionally render components in your applications:

import { useState, useEffect } from 'react';

export function useMediaQuery(query) {
  const [matches, setMatches] = useState(false);

  useEffect(() => {
    const media = window.matchMedia(query);
    if (media.matches !== matches) {
      setMatches(media.matches);
    }
    const listener = () => {
      setMatches(media.matches);
    };
    media.addListener(listener);
    return () => media.removeListener(listener);
  }, [matches, query]);

  return matches;
}

Let’s walk through this. In this custom hook, you have a matches state variable, and we take in a query. In the effect, we check if the query that is passed in matches the window. If it does, we set matches to true. We set an event listener in there as well, to keep that variable in sync with the window changing sizes. The event listener is removed when query changes, when the component using it unmount, or when matches changes.

Whoa. How can I see this in action?

Feel free to use this hook in your projects! You can call it inside your components, for example:

function Page() {
  let isPageWide = useMediaQuery('(min-width: 800px)')

  return <>
    {isPageWide && <UnnecessarySidebar />}
    <ImportantContent />
  </>
}

If you’d like to see it in action in a real project, check out the Jamstack Explorers repo and how we render our Navigation component.

And, if you’d like to learn more about Next.js, check out the course (with more to come) on Jamstack Explorers!