Issue 4795 - Avoid shorthand method syntax where prototype matters

lib/compat.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 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 32 matching lines @@
 let onShutdown = {
   done: false,
   add() {},
   remove() {}
 };
 
 //
 // XPCOM emulation
 //
 
+function nsIFileURL() {}
+function nsIHttpChannel() {}
+
 let Components =
 {
   interfaces:
   {
     nsIFile: {DIRECTORY_TYPE: 0},
-
-    // We don't use the method definition shorthand syntax for these functions

[Sebastian Noack, 2017/01/23 13:54:22]

I had a hard time to understand what is going on here. The problem is that this
is not really a class, but more like a namespace, while nsIFileURL and
nsIHttpChannel are meant to be classes themselves, and in order to define a
class's constructor you have to use the function statement (not the method
shorthand syntax). I wonder whether this comment could better clarify the issue.

[kzar, 2017/01/23 13:59:13]

It surely could, I'm open to suggestions.

[Sebastian Noack, 2017/02/16 12:05:10]

With our just established ESLint configuration this will also cause an error.
How about this:

  function nsIFileURL() {}
  function nsIHttpChannel() {}

  ...

  var Components =
  {
    interfaces:
    {
      ...

      nsIFileURL,
      nsIHttpChannel,

That would also make this comment redundant, IMO.

[kzar, 2017/02/17 09:40:28]

Done.

-    // since that gives them the prototype of undefined which breaks instanceof
-    // checks.
-    nsIFileURL: function() {},
-    nsIHttpChannel: function() {},
-
+    nsIFileURL,
+    nsIHttpChannel,
     nsITimer: {TYPE_REPEATING_SLACK: 0},
     nsIInterfaceRequestor: null,
     nsIChannelEventSink: null
   },
   classes:
   {
     "@mozilla.org/timer;1":
     {
       createInstance() { return new FakeTimer(); }
     },
@@ skipping 187 matching lines @@
   status: -1,
   notificationCallbacks: {},
   loadFlags: 0,
   INHIBIT_CACHING: 0,
   VALIDATE_ALWAYS: 0,
   QueryInterface()
   {
     return this;
   }
 };