Working with JavaScript Media Queries

JavaScript Media Queries: Beyond Window Resize

What springs to mind when you think of media queries? Likely, CSS rules like this:

body {
  background-color: plum;
}

@media (min-width: 768px) {
  body {
    background-color: tomato;
  }
}

CSS media queries are fundamental to responsive design, applying styles based on viewport size, device type, preferences (color scheme, motion), and more. But JavaScript also offers media query capabilities, often valuable for creating responsive plugins or dynamically adjusting elements based on screen conditions.

Unlike CSS, JavaScript's media query handling differs. The core concept remains the same: match conditions and apply actions.

Using matchMedia()

The matchMedia() method determines if a media query matches the current document state. Despite being in the CSS Object Model View Module Working Draft, browser support is excellent.

The usage mirrors CSS: pass a media query string to matchMedia() and check the .matches property.

// Define the query
const mediaQuery = window.matchMedia('(min-width: 768px)');

matchMedia() returns a MediaQueryList object. Its .matches property (read-only Boolean) indicates whether the document matches the query.

// Create a media condition for viewports at least 768px wide
const mediaQuery = window.matchMedia('(min-width: 768px)');
// Check if the media query matches
if (mediaQuery.matches) {
  // Trigger an action
  alert('Media Query Matched!');
}

This handles single checks. For continuous monitoring, we need event listeners.

Listening for Changes

MediaQueryList provides addListener() (and removeListener()) to register a callback function (.onchange event) triggered when the media query status changes. This allows responsive actions to updated conditions.

// Create a condition for viewports at least 768px wide
const mediaQuery = window.matchMedia('(min-width: 768px)');

function handleTabletChange(e) {
  // Check if the media query matches
  if (e.matches) {
    // Perform an action
    console.log('Media Query Matched!');
  } else {
    console.log('Media Query Unmatched!');
  }
}

// Register event listener
mediaQuery.addListener(handleTabletChange);

// Initial check
handleTabletChange(mediaQuery);

addListener() doesn't fire immediately; you must manually call the handler with the MediaQueryList object as an argument.

The "Old" Approach

For comparison, the older method uses a resize event listener with window.innerWidth or window.innerHeight. This is less efficient and less versatile.

function checkMediaQuery() {
  // Check if window inner width is greater than 768px
  if (window.innerWidth > 768) {
    // Perform an action
    console.log('Media Query Matched!');
  }
}

// Add a listener for window resize events
window.addEventListener('resize', checkMediaQuery);

This is performance-intensive and limited to viewport size checks, unlike the more powerful matchMedia() approach.

Conclusion

matchMedia() and MediaQueryList provide robust JavaScript media query handling, enabling both one-time and continuous checks, reacting to changes in various conditions beyond simple viewport size. The older resize event listener remains functional but is less efficient and less feature-rich. The flexibility of matchMedia() makes it the preferred method for modern responsive JavaScript development.

Here's an example demonstrating a capability unavailable with the old method: detecting landscape orientation. This is frequently used in HTML5 game development.

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