Testing media queries

The DOM provides features that make it possible to test the results of a media query programmatically. This is done using the MediaQueryList interface and its methods and properties. Once you've created a MediaQueryList object, you can check the result of the query or, alternatively, receive notifications automatically when the result changes.

Creating a media query list

Before you can evaluate the results of a query, you need to create the MediaQueryList object representing the media query. To do this, use the window.matchMedia method.

For example, if you want to set up a query list that determines whether the device is in landscape or portrait orientation, you can do so like this:

var mql = window.matchMedia("(orientation: portrait)");

Checking the result of a query

Once your media query list has been created, you can check the result of the query by looking at the value of its matches property, which reflects the result of the query:

if (mql.matches) {
  /* The viewport is currently in portrait orientation */
} else {
  /* The viewport is currently in landscape orientation */
}

Receiving query notifications

If you need to be aware of changes to the evaluated result of the query on an ongoing basis, it's more efficient to register a listener than to poll the query's result. To do this, you can call the addListener() method on the MediaQueryList object, specifying an observer that implements the MediaQueryListListener interface:

var mql = window.matchMedia("(orientation: portrait)");
mql.addListener(handleOrientationChange);
handleOrientationChange(mql); 

This code creates the orientation testing media query list, mql, then adds a listener to it. Note that after adding the listener, we actually invoke the listener directly once. This lets our listener perform initial adjustments based on the current device orientation (otherwise, if our code assumes the device is in portrait mode but it's actually in landscape mode at startup, we could have inconsistencies).

The handleOrientationChange() method we implement then would look at the result of the query and handle whatever we need to do on an orientation change:

function handleOrientationChange(mql) {
  if (mql.matches) {
    /* The viewport is currently in portrait orientation */
  } else {
    /* The viewport is currently in landscape orientation */
  }
}

Ending query notifications

When you no longer need to receive notifications about changes to the value of your media query, you can simply call removeListener() on the MediaQueryList:

mql.removeListener(handleOrientationChange);

Browser compatibility

See also

• Media queries
• window.matchMedia()
• MediaQueryList
• MediaQueryListListener