source/js/core/TL.Load.js
function load(type, urls, callback, obj, context) {
    var _finish = function () { finish(type); },
        isCSS   = type === 'css',
        nodes   = [],
        i, len, node, p, pendingUrls, url;

    env || getEnv();

    if (urls) {
      // If urls is a string, wrap it in an array. Otherwise assume it's an
      // array and create a copy of it so modifications won't be made to the
      // original.
      urls = typeof urls === 'string' ? [urls] : urls.concat();

      // Create a request object for each URL. If multiple URLs are specified,
      // the callback will only be executed after all URLs have been loaded.
      //
      // Sadly, Firefox and Opera are the only browsers capable of loading
      // scripts in parallel while preserving execution order. In all other
      // browsers, scripts must be loaded sequentially.
      //
      // All browsers respect CSS specificity based on the order of the link
      // elements in the DOM, regardless of the order in which the stylesheets
      // are actually downloaded.
      if (isCSS || env.async || env.gecko || env.opera) {
        // Load in parallel.
        queue[type].push({
          urls    : urls,
          callback: callback,
          obj     : obj,
          context : context
        });
      } else {
        // Load sequentially.
        for (i = 0, len = urls.length; i < len; ++i) {
          queue[type].push({
            urls    : [urls[i]],
            callback: i === len - 1 ? callback : null, // callback is only added to the last URL
            obj     : obj,
            context : context
          });
        }
      }
    }

    // If a previous load request of this type is currently in progress, we'll
    // wait our turn. Otherwise, grab the next item in the queue.
    if (pending[type] || !(p = pending[type] = queue[type].shift())) {
      return;
    }

    head || (head = doc.head || doc.getElementsByTagName('head')[0]);
    pendingUrls = p.urls;

    for (i = 0, len = pendingUrls.length; i < len; ++i) {
      url = pendingUrls[i];

      if (isCSS) {
          node = env.gecko ? createNode('style') : createNode('link', {
            href: url,
            rel : 'stylesheet'
          });
      } else {
        node = createNode('script', {src: url});
        node.async = false;
      }

      node.className = 'lazyload';
      node.setAttribute('charset', 'utf-8');

      if (env.ie && !isCSS) {
        node.onreadystatechange = function () {
          if (/loaded|complete/.test(node.readyState)) {
            node.onreadystatechange = null;
            _finish();
          }
        };
      } else if (isCSS && (env.gecko || env.webkit)) {
        // Gecko and WebKit don't support the onload event on link nodes.
        if (env.webkit) {
          // In WebKit, we can poll for changes to document.styleSheets to
          // figure out when stylesheets have loaded.
          p.urls[i] = node.href; // resolve relative URLs (or polling won't work)
          pollWebKit();
        } else {
          // In Gecko, we can import the requested URL into a <style> node and
          // poll for the existence of node.sheet.cssRules. Props to Zach
          // Leatherman for calling my attention to this technique.
          node.innerHTML = '@import "' + url + '";';
          pollGecko(node);
        }
      } else {
        node.onload = node.onerror = _finish;
      }

      nodes.push(node);
    }

    for (i = 0, len = nodes.length; i < len; ++i) {
      head.appendChild(nodes[i]);
    }
  }
function load(type, urls, callback, obj, context) {
    var _finish = function () { finish(type); },
        isCSS   = type === 'css',
        nodes   = [],
        i, len, node, p, pendingUrls, url;

    env || getEnv();

    if (urls) {
      // If urls is a string, wrap it in an array. Otherwise assume it's an
      // array and create a copy of it so modifications won't be made to the
      // original.
      urls = typeof urls === 'string' ? [urls] : urls.concat();

      // Create a request object for each URL. If multiple URLs are specified,
      // the callback will only be executed after all URLs have been loaded.
      //
      // Sadly, Firefox and Opera are the only browsers capable of loading
      // scripts in parallel while preserving execution order. In all other
      // browsers, scripts must be loaded sequentially.
      //
      // All browsers respect CSS specificity based on the order of the link
      // elements in the DOM, regardless of the order in which the stylesheets
      // are actually downloaded.
      if (isCSS || env.async || env.gecko || env.opera) {
        // Load in parallel.
        queue[type].push({
          urls    : urls,
          callback: callback,
          obj     : obj,
          context : context
        });
      } else {
        // Load sequentially.
        for (i = 0, len = urls.length; i < len; ++i) {
          queue[type].push({
            urls    : [urls[i]],
            callback: i === len - 1 ? callback : null, // callback is only added to the last URL
            obj     : obj,
            context : context
          });
        }
      }
    }

    // If a previous load request of this type is currently in progress, we'll
    // wait our turn. Otherwise, grab the next item in the queue.
    if (pending[type] || !(p = pending[type] = queue[type].shift())) {
      return;
    }

    head || (head = doc.head || doc.getElementsByTagName('head')[0]);
    pendingUrls = p.urls;

    for (i = 0, len = pendingUrls.length; i < len; ++i) {
      url = pendingUrls[i];

      if (isCSS) {
          node = env.gecko ? createNode('style') : createNode('link', {
            href: url,
            rel : 'stylesheet'
          });
      } else {
        node = createNode('script', {src: url});
        node.async = false;
      }

      node.className = 'lazyload';
      node.setAttribute('charset', 'utf-8');

      if (env.ie && !isCSS) {
        node.onreadystatechange = function () {
          if (/loaded|complete/.test(node.readyState)) {
            node.onreadystatechange = null;
            _finish();
          }
        };
      } else if (isCSS && (env.gecko || env.webkit)) {
        // Gecko and WebKit don't support the onload event on link nodes.
        if (env.webkit) {
          // In WebKit, we can poll for changes to document.styleSheets to
          // figure out when stylesheets have loaded.
          p.urls[i] = node.href; // resolve relative URLs (or polling won't work)
          pollWebKit();
        } else {
          // In Gecko, we can import the requested URL into a <style> node and
          // poll for the existence of node.sheet.cssRules. Props to Zach
          // Leatherman for calling my attention to this technique.
          node.innerHTML = '@import "' + url + '";';
          pollGecko(node);
        }
      } else {
        node.onload = node.onerror = _finish;
      }

      nodes.push(node);
    }

    for (i = 0, len = nodes.length; i < len; ++i) {
      head.appendChild(nodes[i]);
    }
  }
function load ( type , urls , callback , obj , context ) { var _finish = function ( ) { finish ( type ) ; } , isCSS = type === 'css' , nodes = [ ] , i , len , node , p , pendingUrls , url ; env || getEnv ( ) ; if ( urls ) { // If urls is a string, wrap it in an array. Otherwise assume it's an // array and create a copy of it so modifications won't be made to the // original. urls = typeof urls === 'string' ? [ urls ] : urls . concat ( ) ; // Create a request object for each URL. If multiple URLs are specified, // the callback will only be executed after all URLs have been loaded. // // Sadly, Firefox and Opera are the only browsers capable of loading // scripts in parallel while preserving execution order. In all other // browsers, scripts must be loaded sequentially. // // All browsers respect CSS specificity based on the order of the link // elements in the DOM, regardless of the order in which the stylesheets // are actually downloaded. if ( isCSS || env . async || env . gecko || env . opera ) { // Load in parallel. queue [ type ] . push ( { urls : urls , callback : callback , obj : obj , context : context } ) ; } else { // Load sequentially. for ( i = 0 , len = urls . length ; i < len ; ++ i ) { queue [ type ] . push ( { urls : [ urls [ i ] ] , callback : i === len - 1 ? callback : null , // callback is only added to the last URL obj : obj , context : context } ) ; } } } // If a previous load request of this type is currently in progress, we'll // wait our turn. Otherwise, grab the next item in the queue. if ( pending [ type ] || ! ( p = pending [ type ] = queue [ type ] . shift ( ) ) ) { return ; } head || ( head = doc . head || doc . getElementsByTagName ( 'head' ) [ 0 ] ) ; pendingUrls = p . urls ; for ( i = 0 , len = pendingUrls . length ; i < len ; ++ i ) { url = pendingUrls [ i ] ; if ( isCSS ) { node = env . gecko ? createNode ( 'style' ) : createNode ( 'link' , { href : url , rel : 'stylesheet' } ) ; } else { node = createNode ( 'script' , { src : url } ) ; node . async = false ; } node . className = 'lazyload' ; node . setAttribute ( 'charset' , 'utf-8' ) ; if ( env . ie && ! isCSS ) { node . onreadystatechange = function ( ) { if ( / loaded|complete / . test ( node . readyState ) ) { node . onreadystatechange = null ; _finish ( ) ; } } ; } else if ( isCSS && ( env . gecko || env . webkit ) ) { // Gecko and WebKit don't support the onload event on link nodes. if ( env . webkit ) { // In WebKit, we can poll for changes to document.styleSheets to // figure out when stylesheets have loaded. p . urls [ i ] = node . href ; // resolve relative URLs (or polling won't work) pollWebKit ( ) ; } else { // In Gecko, we can import the requested URL into a <style> node and // poll for the existence of node.sheet.cssRules. Props to Zach // Leatherman for calling my attention to this technique. node . innerHTML = '@import "' + url + '";' ; pollGecko ( node ) ; } } else { node . onload = node . onerror = _finish ; } nodes . push ( node ) ; } for ( i = 0 , len = nodes . length ; i < len ; ++ i ) { head . appendChild ( nodes [ i ] ) ; } }
Loads the specified resources, or the next resource of the specified type
in the queue if no resources are specified. If a resource of the specified
type is already being loaded, the new request will be queued until the
first request has been finished.

When an array of resource URLs is specified, those URLs will be loaded in
parallel if it is possible to do so while preserving execution order. All
browsers support parallel loading of CSS, but only Firefox and Opera
support parallel loading of scripts. In other browsers, scripts will be
queued and loaded one at a time to ensure correct execution order.

@method load
@param {String} type resource type ('css' or 'js')
@param {String|Array} urls (optional) URL or array of URLs to load
@param {Function} callback (optional) callback function to execute when the
resource is loaded
@param {Object} obj (optional) object to pass to the callback function
@param {Object} context (optional) if provided, the callback function will
be executed in this object's context
@private
Loads the specified resources or the next resource of the specified type in the queue if no resources are specified . If a resource of the specified type is already being loaded the new request will be queued until the first request has been finished .