The Window interface's matchMedia() method returns a new MediaQueryList object that can then be used to determine if the document matches the media query string, as well as to monitor the document to detect when it matches (or stops matching) that media query.

mediaQueryString

A string specifying the media query to parse into a MediaQueryList.

A new MediaQueryList object for the media query. Use this object's properties and events to detect matches and to monitor for changes to those matches over time.

You can use the returned media query to perform both instantaneous and event-driven checks to see if the document matches the media query.

To perform a one-time, instantaneous check to see if the document matches the media query, look at the value of the matches property, which will be true if the document meets the media query's requirements.

If you need to be kept aware of whether or not the document matches the media query at all times, you can instead watch for the change event to be delivered to the object. There's a good example of this in the article on Window.devicePixelRatio.

This example runs the media query (max-width: 600px) and displays the value of the resulting MediaQueryList's matches property in a <span>; as a result, the output will say "true" if the viewport is less than or equal to 600 pixels wide, and will say "false" if the window is wider than that.

let mql = window.matchMedia("(max-width: 600px)");

document.querySelector(".mq-value").innerText = mql.matches;

The JavaScript code passes the media query to match into matchMedia() to compile it, then sets the <span>'s innerText to the value of the results' matches property, so that it indicates whether or not the document matches the media query at the moment the page was loaded.

<span class="mq-value"></span>

A simple <span> to receive the output.

See Testing media queries programmatically for additional code examples.

• Media queries
• Using media queries from code
• MediaQueryList