matchMedia.addListener.js

/*! matchMedia() polyfill addListener/removeListener extension. Author & copyright (c) 2012: Scott Jehl. MIT license */
(function(){
    // Bail out for browsers that have addListener support
    if (window.matchMedia && window.matchMedia('all').addListener) {
        return false;
    }

    var localMatchMedia = window.matchMedia,
        hasMediaQueries = localMatchMedia('only all').matches,
        isListening     = false,
        timeoutID       = 0,    // setTimeout for debouncing 'handleChange'
        queries         = [],   // Contains each 'mql' and associated 'listeners' if 'addListener' is used
        handleChange    = function(evt) {
            // Debounce
            clearTimeout(timeoutID);

            timeoutID = setTimeout(function() {
                for (var i = 0, il = queries.length; i < il; i++) {
                    var mql         = queries[i].mql,
                        listeners   = queries[i].listeners || [],
                        matches     = localMatchMedia(mql.media).matches;

                    // Update mql.matches value and call listeners
                    // Fire listeners only if transitioning to or from matched state
                    if (matches !== mql.matches) {
                        mql.matches = matches;

                        for (var j = 0, jl = listeners.length; j < jl; j++) {
                            listeners[j].call(window, mql);
                        }
                    }
                }
            }, 30);
        };

    window.matchMedia = function(media) {
        var mql         = localMatchMedia(media),
            listeners   = [],
            index       = 0;

        mql.addListener = function(listener) {
            // Changes would not occur to css media type so return now (Affects IE <= 8)
            if (!hasMediaQueries) {
                return;
            }

            // Set up 'resize' listener for browsers that support CSS3 media queries (Not for IE <= 8)
            // There should only ever be 1 resize listener running for performance
            if (!isListening) {
                isListening = true;
                window.addEventListener('resize', handleChange, true);
            }

            // Push object only if it has not been pushed already
            if (index === 0) {
                index = queries.push({
                    mql         : mql,
                    listeners   : listeners
                });
            }

            listeners.push(listener);
        };

        mql.removeListener = function(listener) {
            for (var i = 0, il = listeners.length; i < il; i++){
                if (listeners[i] === listener){
                    listeners.splice(i, 1);
                }
            }
        };

        return mql;
    };
}());