Issue 5137 - [emscripten] Added basic filter storage implementation

lib/subscriptionClasses.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 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
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 "use strict";
 
-const compiled = require("compiled");
-for (let cls of [
-  "Subscription", "SpecialSubscription", "DownloadableSubscription"
-])
-{
-  exports[cls] = compiled[cls];
-}
+const {Subscription, SpecialSubscription, DownloadableSubscription} =
+    require("compiled");
+
+/**
+ * This property allows iterating over the list of filters. It will delete
+ * references automatically at the end of the current loop iteration. If you
+ * need persistent references or element access by position you should use
+ * Subscription.filterAt() instead.
+ * @type {Iterable}
+ */
+Object.defineProperty(Subscription.prototype, "filters", {
+  enumerable: true,
+  get()
+  {
+    return {
+      [Symbol.iterator]: function*()
+      {
+        for (let i = 0, l = this.filterCount; i < l; i++)
+        {
+          let filter = this.filterAt(i);
+          try
+          {
+            yield filter;
+          }
+          finally
+          {
+            filter.delete();
+          }
+        }
+      }.bind(this)
+    };
+  }
+});
+
+exports.Subscription = Subscription;
+exports.SpecialSubscription = SpecialSubscription;
+exports.DownloadableSubscription = DownloadableSubscription;