Issue 6559 - Use maps and sets where appropriate

lib/downloader.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 30 matching lines @@
  */
 exports.Downloader = function(dataSource, initialDelay, checkInterval)
 {
   this.dataSource = dataSource;
   this._timer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
   this._timer.initWithCallback(() =>
   {
     this._timer.delay = checkInterval;
     this._doCheck();
   }, initialDelay, Ci.nsITimer.TYPE_REPEATING_SLACK);
-  this._downloading = Object.create(null);
+  this._downloading = new Set();
 };
 Downloader.prototype =
 {
   /**
    * Timer triggering the downloads.
    * @type {nsITimer}
    */
   _timer: null,
 
   /**
-   * Map containing the URLs of objects currently being downloaded as its keys.
+   * Set containing the URLs of objects currently being downloaded.
+   * @type {Set.<string>}
    */
   _downloading: null,
 
   /**
    * Function that will yield downloadable objects on each check.
    * @type {Function}
    */
   dataSource: null,
 
   /**
@@ skipping 102 matching lines @@
     this._timer.cancel();
   },
 
   /**
    * Checks whether an address is currently being downloaded.
    * @param {string} url
    * @return {boolean}
    */
   isDownloading(url)
   {
-    return url in this._downloading;
+    return this._downloading.has(url);
   },
 
   /**
    * Starts downloading for an object.
    * @param {Downloadable} downloadable
    */
   download(downloadable)
   {
     // Make sure to detach download from the current execution context
     Utils.runAsync(this._download.bind(this, downloadable, 0));
@@ skipping 98 matching lines @@
     catch (e)
     {
       Cu.reportError(e);
     }
 
     request.addEventListener("error", event =>
     {
       if (onShutdown.done)
         return;
 
-      delete this._downloading[downloadable.url];
+      this._downloading.delete(downloadable.url);
       errorCallback("synchronize_connection_error");
     }, false);
 
     request.addEventListener("load", event =>
     {
       if (onShutdown.done)
         return;
 
-      delete this._downloading[downloadable.url];
+      this._downloading.delete(downloadable.url);
 
       // Status will be 0 for non-HTTP requests
       if (request.status && request.status != 200)
       {
         errorCallback("synchronize_connection_error");
         return;
       }
 
       downloadable.downloadCount++;
 
       this.onDownloadSuccess(
         downloadable, request.responseText, errorCallback,
         url =>
         {
           if (redirects >= this.maxRedirects)
             errorCallback("synchronize_connection_error");
           else
           {
             downloadable.redirectURL = url;
             this._download(downloadable, redirects + 1);
           }
         }
       );
     });
 
     request.send(null);
 
-    this._downloading[downloadable.url] = true;
+    this._downloading.add(downloadable.url);
     if (this.onDownloadStarted)
       this.onDownloadStarted(downloadable);
   },
 
   /**
    * Produces a soft and a hard expiration interval for a given supplied
    * expiration interval.
    * @param {number} interval
    * @return {Array} soft and hard expiration interval
    */
@@ skipping 60 matching lines @@
    * @type {number}
    */
   hardExpiration: 0,
 
   /**
    * Number indicating how often the object was downloaded.
    * @type {number}
    */
   downloadCount: 0
 };