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/*jslint browser: true, eqeqeq: true, bitwise: true, newcap: true, immed: true, regexp: false */ |
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/** |
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LazyLoad makes it easy and painless to lazily load one or more external |
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JavaScript or CSS files on demand either during or after the rendering of a web |
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page. |
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Supported browsers include Firefox 2+, IE6+, Safari 3+ (including Mobile |
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Safari), Google Chrome, and Opera 9+. Other browsers may or may not work and |
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are not officially supported. |
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Visit https://github.com/rgrove/lazyload/ for more info. |
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Copyright (c) 2011 Ryan Grove <ryan@wonko.com> |
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All rights reserved. |
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Permission is hereby granted, free of charge, to any person obtaining a copy of |
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this software and associated documentation files (the 'Software'), to deal in |
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the Software without restriction, including without limitation the rights to |
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use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of |
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the Software, and to permit persons to whom the Software is furnished to do so, |
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subject to the following conditions: |
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The above copyright notice and this permission notice shall be included in all |
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copies or substantial portions of the Software. |
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THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR |
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS |
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FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR |
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COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER |
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IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN |
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CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. |
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@module lazyload |
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@class LazyLoad |
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@static |
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@version 2.0.3 (git) |
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*/ |
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LazyLoad = (function (doc) { |
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// -- Private Variables ------------------------------------------------------ |
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// User agent and feature test information. |
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var env, |
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// Reference to the <head> element (populated lazily). |
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head, |
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// Requests currently in progress, if any. |
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pending = {}, |
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// Number of times we've polled to check whether a pending stylesheet has |
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// finished loading. If this gets too high, we're probably stalled. |
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pollCount = 0, |
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// Queued requests. |
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queue = {css: [], js: []}, |
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// Reference to the browser's list of stylesheets. |
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styleSheets = doc.styleSheets; |
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// -- Private Methods -------------------------------------------------------- |
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/** |
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Creates and returns an HTML element with the specified name and attributes. |
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@method createNode |
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@param {String} name element name |
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@param {Object} attrs name/value mapping of element attributes |
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@return {HTMLElement} |
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@private |
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*/ |
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function createNode(name, attrs) { |
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var node = doc.createElement(name), attr; |
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for (attr in attrs) { |
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if (attrs.hasOwnProperty(attr)) { |
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node.setAttribute(attr, attrs[attr]); |
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} |
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} |
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return node; |
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} |
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/** |
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Called when the current pending resource of the specified type has finished |
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loading. Executes the associated callback (if any) and loads the next |
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resource in the queue. |
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@method finish |
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@param {String} type resource type ('css' or 'js') |
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@private |
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*/ |
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function finish(type) { |
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var p = pending[type], |
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callback, |
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urls; |
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if (p) { |
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callback = p.callback; |
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urls = p.urls; |
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urls.shift(); |
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pollCount = 0; |
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// If this is the last of the pending URLs, execute the callback and |
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// start the next request in the queue (if any). |
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if (!urls.length) { |
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callback && callback.call(p.context, p.obj); |
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pending[type] = null; |
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queue[type].length && load(type); |
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} |
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} |
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} |
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/** |
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Populates the <code>env</code> variable with user agent and feature test |
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information. |
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@method getEnv |
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@private |
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*/ |
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function getEnv() { |
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var ua = navigator.userAgent; |
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env = { |
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// True if this browser supports disabling async mode on dynamically |
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// created script nodes. See |
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// http://wiki.whatwg.org/wiki/Dynamic_Script_Execution_Order |
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async: doc.createElement('script').async === true |
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}; |
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(env.webkit = /AppleWebKit\//.test(ua)) |
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|| (env.ie = /MSIE/.test(ua)) |
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|| (env.opera = /Opera/.test(ua)) |
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|| (env.gecko = /Gecko\//.test(ua)) |
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|| (env.unknown = true); |
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} |
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/** |
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Loads the specified resources, or the next resource of the specified type |
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in the queue if no resources are specified. If a resource of the specified |
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type is already being loaded, the new request will be queued until the |
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first request has been finished. |
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When an array of resource URLs is specified, those URLs will be loaded in |
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parallel if it is possible to do so while preserving execution order. All |
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browsers support parallel loading of CSS, but only Firefox and Opera |
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support parallel loading of scripts. In other browsers, scripts will be |
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queued and loaded one at a time to ensure correct execution order. |
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@method load |
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@param {String} type resource type ('css' or 'js') |
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@param {String|Array} urls (optional) URL or array of URLs to load |
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@param {Function} callback (optional) callback function to execute when the |
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resource is loaded |
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@param {Object} obj (optional) object to pass to the callback function |
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@param {Object} context (optional) if provided, the callback function will |
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be executed in this object's context |
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@private |
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*/ |
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function load(type, urls, callback, obj, context) { |
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var _finish = function () { finish(type); }, |
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isCSS = type === 'css', |
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nodes = [], |
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i, len, node, p, pendingUrls, url; |
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env || getEnv(); |
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if (urls) { |
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// If urls is a string, wrap it in an array. Otherwise assume it's an |
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// array and create a copy of it so modifications won't be made to the |
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// original. |
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urls = typeof urls === 'string' ? [urls] : urls.concat(); |
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// Create a request object for each URL. If multiple URLs are specified, |
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// the callback will only be executed after all URLs have been loaded. |
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// |
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// Sadly, Firefox and Opera are the only browsers capable of loading |
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// scripts in parallel while preserving execution order. In all other |
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// browsers, scripts must be loaded sequentially. |
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// |
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// All browsers respect CSS specificity based on the order of the link |
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// elements in the DOM, regardless of the order in which the stylesheets |
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// are actually downloaded. |
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if (isCSS || env.async || env.gecko || env.opera) { |
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// Load in parallel. |
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queue[type].push({ |
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urls : urls, |
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callback: callback, |
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obj : obj, |
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context : context |
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}); |
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} else { |
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// Load sequentially. |
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for (i = 0, len = urls.length; i < len; ++i) { |
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queue[type].push({ |
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urls : [urls[i]], |
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callback: i === len - 1 ? callback : null, // callback is only added to the last URL |
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obj : obj, |
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context : context |
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}); |
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} |
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} |
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} |
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// If a previous load request of this type is currently in progress, we'll |
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// wait our turn. Otherwise, grab the next item in the queue. |
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if (pending[type] || !(p = pending[type] = queue[type].shift())) { |
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return; |
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} |
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head || (head = doc.head || doc.getElementsByTagName('head')[0]); |
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pendingUrls = p.urls; |
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for (i = 0, len = pendingUrls.length; i < len; ++i) { |
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url = pendingUrls[i]; |
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if (isCSS) { |
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node = env.gecko ? createNode('style') : createNode('link', { |
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href: url, |
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rel : 'stylesheet' |
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}); |
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} else { |
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node = createNode('script', {src: url}); |
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node.async = false; |
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} |
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node.className = 'lazyload'; |
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node.setAttribute('charset', 'utf-8'); |
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if (env.ie && !isCSS) { |
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node.onreadystatechange = function () { |
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if (/loaded|complete/.test(node.readyState)) { |
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node.onreadystatechange = null; |
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_finish(); |
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} |
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}; |
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} else if (isCSS && (env.gecko || env.webkit)) { |
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// Gecko and WebKit don't support the onload event on link nodes. |
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if (env.webkit) { |
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// In WebKit, we can poll for changes to document.styleSheets to |
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// figure out when stylesheets have loaded. |
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p.urls[i] = node.href; // resolve relative URLs (or polling won't work) |
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pollWebKit(); |
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} else { |
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// In Gecko, we can import the requested URL into a <style> node and |
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// poll for the existence of node.sheet.cssRules. Props to Zach |
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// Leatherman for calling my attention to this technique. |
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node.innerHTML = '@import "' + url + '";'; |
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pollGecko(node); |
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} |
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} else { |
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node.onload = node.onerror = _finish; |
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} |
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nodes.push(node); |
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} |
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for (i = 0, len = nodes.length; i < len; ++i) { |
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head.appendChild(nodes[i]); |
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} |
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} |
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/** |
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Begins polling to determine when the specified stylesheet has finished loading |
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in Gecko. Polling stops when all pending stylesheets have loaded or after 10 |
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seconds (to prevent stalls). |
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Thanks to Zach Leatherman for calling my attention to the @import-based |
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cross-domain technique used here, and to Oleg Slobodskoi for an earlier |
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same-domain implementation. See Zach's blog for more details: |
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http://www.zachleat.com/web/2010/07/29/load-css-dynamically/ |
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@method pollGecko |
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@param {HTMLElement} node Style node to poll. |
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@private |
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*/ |
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function pollGecko(node) { |
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var hasRules; |
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try { |
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// We don't really need to store this value or ever refer to it again, but |
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// if we don't store it, Closure Compiler assumes the code is useless and |
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// removes it. |
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hasRules = !!node.sheet.cssRules; |
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} catch (ex) { |
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// An exception means the stylesheet is still loading. |
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pollCount += 1; |
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if (pollCount < 200) { |
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setTimeout(function () { pollGecko(node); }, 50); |
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} else { |
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// We've been polling for 10 seconds and nothing's happened. Stop |
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// polling and finish the pending requests to avoid blocking further |
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// requests. |
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hasRules && finish('css'); |
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} |
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return; |
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} |
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// If we get here, the stylesheet has loaded. |
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finish('css'); |
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} |
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/** |
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Begins polling to determine when pending stylesheets have finished loading |
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in WebKit. Polling stops when all pending stylesheets have loaded or after 10 |
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seconds (to prevent stalls). |
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@method pollWebKit |
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@private |
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*/ |
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function pollWebKit() { |
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var css = pending.css, i; |
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if (css) { |
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i = styleSheets.length; |
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// Look for a stylesheet matching the pending URL. |
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while (--i >= 0) { |
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if (styleSheets[i].href === css.urls[0]) { |
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finish('css'); |
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break; |
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} |
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} |
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pollCount += 1; |
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if (css) { |
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if (pollCount < 200) { |
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setTimeout(pollWebKit, 50); |
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} else { |
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// We've been polling for 10 seconds and nothing's happened, which may |
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// indicate that the stylesheet has been removed from the document |
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// before it had a chance to load. Stop polling and finish the pending |
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// request to prevent blocking further requests. |
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finish('css'); |
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} |
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} |
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} |
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} |
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return { |
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/** |
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Requests the specified CSS URL or URLs and executes the specified |
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callback (if any) when they have finished loading. If an array of URLs is |
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specified, the stylesheets will be loaded in parallel and the callback |
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will be executed after all stylesheets have finished loading. |
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@method css |
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@param {String|Array} urls CSS URL or array of CSS URLs to load |
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@param {Function} callback (optional) callback function to execute when |
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the specified stylesheets are loaded |
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@param {Object} obj (optional) object to pass to the callback function |
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@param {Object} context (optional) if provided, the callback function |
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will be executed in this object's context |
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@static |
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*/ |
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css: function (urls, callback, obj, context) { |
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load('css', urls, callback, obj, context); |
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}, |
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/** |
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Requests the specified JavaScript URL or URLs and executes the specified |
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callback (if any) when they have finished loading. If an array of URLs is |
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specified and the browser supports it, the scripts will be loaded in |
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parallel and the callback will be executed after all scripts have |
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finished loading. |
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Currently, only Firefox and Opera support parallel loading of scripts while |
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preserving execution order. In other browsers, scripts will be |
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queued and loaded one at a time to ensure correct execution order. |
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@method js |
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@param {String|Array} urls JS URL or array of JS URLs to load |
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@param {Function} callback (optional) callback function to execute when |
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the specified scripts are loaded |
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@param {Object} obj (optional) object to pass to the callback function |
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@param {Object} context (optional) if provided, the callback function |
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will be executed in this object's context |
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@static |
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*/ |
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js: function (urls, callback, obj, context) { |
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load('js', urls, callback, obj, context); |
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} |
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}; |
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})(this.document); |