2012-10-28 21:40:07 +00:00
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/**
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* Polyfill the behavior of window.matchMedia.
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*
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* @see http://dev.w3.org/csswg/cssom-view/#widl-Window-matchMedia-MediaQueryList-DOMString-query
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*
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* Test whether a CSS media type or media query applies. Register listeners
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* to MediaQueryList objects.
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*
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* Adapted from https://github.com/paulirish/matchMedia.js with the addition
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* of addListener and removeListener. The polyfill referenced above uses
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* polling to trigger registered listeners on matchMedia tests.
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* This polyfill triggers tests on window resize and orientationchange.
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*/
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window.matchMedia = window.matchMedia || (function (doc, window) {
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"use strict";
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var docElem = doc.documentElement;
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var refNode = docElem.firstElementChild || docElem.firstChild;
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// fakeBody required for <FF4 when executed in <head>.
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var fakeBody = doc.createElement("body");
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var div = doc.createElement("div");
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div.id = "mq-test-1";
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div.style.cssText = "position:absolute;top:-100em";
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fakeBody.style.background = "none";
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fakeBody.appendChild(div);
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/**
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* A replacement for the native MediaQueryList object.
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*
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* @param {String} q
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* A media query e.g. "screen" or "screen and (min-width: 28em)".
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*/
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function MediaQueryList (q) {
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this.media = q;
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this.matches = false;
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this.check.call(this);
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}
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/**
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* Polyfill the addListener and removeListener methods.
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*/
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MediaQueryList.prototype = {
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listeners: [],
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/**
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* Perform the media query application check.
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*/
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check: function () {
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var isApplied;
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div.innerHTML = "­<style media=\"" + this.media + "\"> #mq-test-1 {width: 42px;}</style>";
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docElem.insertBefore(fakeBody, refNode);
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isApplied = div.offsetWidth === 42;
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docElem.removeChild(fakeBody);
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this.matches = isApplied;
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},
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/**
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* Polyfill the addListener method of the MediaQueryList object.
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*
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* @param {Function} callback
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* The callback to be invoked when the media query is applicable.
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*
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* @return {Object MediaQueryList}
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* A MediaQueryList object that indicates whether the registered media
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* query applies. The matches property is true when the media query
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* applies and false when not. The original media query is referenced in
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* the media property.
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*/
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addListener: function (callback) {
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var handler = (function (mql, debounced) {
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return function () {
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2012-10-29 21:02:05 +00:00
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// Only execute the callback if the state has changed.
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var oldstate = mql.matches;
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2012-10-28 21:40:07 +00:00
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mql.check();
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2012-10-29 21:02:05 +00:00
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if (oldstate != mql.matches) {
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debounced.call(mql, mql);
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}
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2012-10-28 21:40:07 +00:00
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};
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}(this, debounce(callback, 250)));
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this.listeners.push({
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'callback': callback,
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'handler': handler
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});
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// Associate the handler to the resize and orientationchange events.
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if ('addEventListener' in window) {
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window.addEventListener('resize', handler);
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window.addEventListener('orientationchange', handler);
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}
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else if ('attachEvent' in window) {
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window.attachEvent('onresize', handler);
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window.attachEvent('onorientationchange', handler);
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}
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},
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/**
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* Polyfill the removeListener method of the MediaQueryList object.
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*
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* @param {Function} callback
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* The callback to be removed from the set of listeners.
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*/
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removeListener: function (callback) {
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for (var i = 0, listeners = this.listeners; i < listeners.length; i++) {
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if (listeners[i].callback === callback) {
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// Disassociate the handler to the resize and orientationchange events.
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if ('removeEventListener' in window) {
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window.removeEventListener('resize', listeners[i].handler);
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window.removeEventListener('orientationchange', listeners[i].handler);
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}
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else if ('detachEvent' in window) {
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window.detachEvent('onresize', listeners[i].handler);
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window.detachEvent('onorientationchange', listeners[i].handler);
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}
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listeners.splice(i, 1);
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}
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}
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}
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};
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/**
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* Limits the invocations of a function in a given time frame.
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*
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* @param {Function} callback
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* The function to be invoked.
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*
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* @param {Number} wait
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* The time period within which the callback function should only be
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* invoked once. For example if the wait period is 250ms, then the callback
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* will only be called at most 4 times per second.
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*/
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function debounce (callback, wait) {
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var timeout, result;
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return function () {
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var context = this;
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var args = arguments;
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var later = function () {
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timeout = null;
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result = callback.apply(context, args);
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};
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window.clearTimeout(timeout);
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timeout = window.setTimeout(later, wait);
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return result;
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};
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}
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/**
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* Return a MediaQueryList.
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*
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* @param {String} q
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* A media query e.g. "screen" or "screen and (min-width: 28em)". The media
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* query is checked for applicability before the object is returned.
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*/
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return function (q) {
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// Build a new MediaQueryList object with the result of the check.
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return new MediaQueryList(q);
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};
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}(document, window));
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