window.devicePixelRatio change listener

Question

window.devicePixelRatio will return 1 or 2 depending on if I'm using my retina monitor or standard. If I drag the window between the two monitors, this property will change. Is there a way I can have a listener fire when the change occurs?

Answer 1

You can listen to a media query with matchMedia that will tell you when the devicePixelRatio goes past a certain barrier (unfortunately not for arbitrary scale changes).

e.g:

window.matchMedia('screen and (min-resolution: 2dppx)').
    addListener(function(e) {
      if (e.matches) {
        /* devicePixelRatio >= 2 */
      } else {
        /* devicePixelRatio < 2 */
      }
    });

The listener will be called when you drag a window between monitors, and when plugging in or unplugging an external non-retina monitor (if it causes the window to move from a retina to non-retina screen or vice-versa).

window.matchMedia is supported in IE10+, and all other modern browsers.

References: https://code.google.com/p/chromium/issues/detail?id=123694, MDN on min-resolution