modernizr/src/mq.js

Modernizr is a JavaScript library that detects HTML5 and CSS3 features in the user’s browser.

define(['ModernizrProto', 'injectElementWithStyles'], function(ModernizrProto, injectElementWithStyles) {
  /**
   * Modernizr.mq tests a given media query, live against the current state of the window
   * adapted from matchMedia polyfill by Scott Jehl and Paul Irish
   * gist.github.com/786768
   *
   * @memberof Modernizr
   * @name Modernizr.mq
   * @optionName Modernizr.mq()
   * @optionProp mq
   * @access public
   * @function mq
   * @param {string} mq - String of the media query we want to test
   * @returns {boolean}
   * @example
   * Modernizr.mq allows for you to programmatically check if the current browser
   * window state matches a media query.
   *
   * ```js
   *  var query = Modernizr.mq('(min-width: 900px)');
   *
   *  if (query) {
   *    // the browser window is larger than 900px
   *  }
   * ```
   *
   * Only valid media queries are supported, therefore you must always include values
   * with your media query
   *
   * ```js
   * // good
   *  Modernizr.mq('(min-width: 900px)');
   *
   * // bad
   *  Modernizr.mq('min-width');
   * ```
   *
   * If you would just like to test that media queries are supported in general, use
   *
   * ```js
   *  Modernizr.mq('only all'); // true if MQ are supported, false if not
   * ```
   *
   *
   * Note that if the browser does not support media queries (e.g. old IE) mq will
   * always return false.
   */

  var mq = (function() {
    var matchMedia = window.matchMedia || window.msMatchMedia;
    if (matchMedia) {
      return function(mq) {
        var mql = matchMedia(mq);
        return mql && mql.matches || false;
      };
    }

    return function(mq) {
      var bool = false;

      injectElementWithStyles('@media ' + mq + ' { #modernizr { position: absolute; } }', function(node) {
        bool = (window.getComputedStyle ?
                window.getComputedStyle(node, null) :
                node.currentStyle).position == 'absolute';
      });

      return bool;
    };
  })();


  ModernizrProto.mq = mq;

  return mq;
});