chrome/browser/resources/downloads/throttled_icon_loader.js

   1 // Copyright 2015 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 /** @typedef {{img: HTMLImageElement, url: string}} */
   6 var LoadIconRequest;
   7
   8 cr.define('downloads', function() {
   9   /**
  10    * @param {number} maxAllowed The maximum number of simultaneous downloads
  11    *     allowed.
  12    * @constructor
  13    */
  14   function ThrottledIconLoader(maxAllowed) {
  15     assert(maxAllowed > 0);
  16
  17     /** @private {number} */
  18     this.maxAllowed_ = maxAllowed;
  19
  20     /** @private {!Array<!LoadIconRequest>} */
  21     this.requests_ = [];
  22   }
  23
  24   ThrottledIconLoader.prototype = {
  25     /** @private {number} */
  26     loading_: 0,
  27
  28     /**
  29      * Load the provided |url| into |img.src| after appending ?scale=.
  30      * @param {!HTMLImageElement} img An <img> to show the loaded image in.
  31      * @param {string} url A remote image URL to load.
  32      */
  33     loadScaledIcon: function(img, url) {
  34       var scaledUrl = url + '?scale=' + window.devicePixelRatio + 'x';
  35       if (img.src == scaledUrl)
  36         return;
  37
  38       this.requests_.push({img: img, url: scaledUrl});
  39       this.loadNextIcon_();
  40     },
  41
  42     /** @private */
  43     loadNextIcon_: function() {
  44       if (this.loading_ > this.maxAllowed_ || !this.requests_.length)
  45         return;
  46
  47       var request = this.requests_.shift();
  48       var img = request.img;
  49
  50       img.onabort = img.onerror = img.onload = function() {
  51         this.loading_--;
  52         this.loadNextIcon_();
  53       }.bind(this);
  54
  55       this.loading_++;
  56       img.src = request.url;
  57     },
  58   };
  59
  60   return {ThrottledIconLoader: ThrottledIconLoader};
  61 });