Getting notified in JavaScript when a Media Query changes

Media queries are awesome and well used in modern web development. But how can one notify JavaScript if a certain media query is met.

There is a window listener called: matchMedia, and it does exactly this!

This is what we will be making today:

JavaScript Media Query Changes

To use matchMedia we call the following:

var mediaQuery = window.matchMedia('(max-width: 500px)');

To use it we can add listeners to it:

mediaQuery.addListener(console.log);

Now if we size our screen with the console open it will fire a console log each this this media queries matches.

The return will have a MediaQueryListEvent, which contains a value called matches to say true or false.

Console logs are cool, but it doesn't really do much for us, so we can also attach a function:

mediaQuery.addListener(alertMe);

function alertMe(e) {
  if (e.matches) {
    document.body.style.backgroundColor = 'green';
  } else {
    document.body.style.backgroundColor = 'red';
  }
}

Now, if we resize and hit the media query, our screen will turn green or red depending on yes or no.

See this Codepen for a demo.

More on MediaQueryList here MDN Web Docs

Browser Support

This function has really good support! For a novice function, definitely, one to use in projects.

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