Noissue - Make _listeners a Set object

ext/common.js

Index: ext/common.js
diff --git a/ext/common.js b/ext/common.js
index 173bbaf443e1fc9eb0b5736e403e35a79c4755d7..1d66b1ed163c0af4bf585dd10c7b9a8d4f52362c 100644
--- a/ext/common.js
+++ b/ext/common.js
@@ -23,24 +23,21 @@
 
   let EventTarget = ext._EventTarget = function()
   {
-    this._listeners = [];
+    this._listeners = new Set();
   };
   EventTarget.prototype = {
     addListener(listener)
     {
-      if (this._listeners.indexOf(listener) == -1)
-        this._listeners.push(listener);
+      this._listeners.add(listener);
     },
     removeListener(listener)
     {
-      let idx = this._listeners.indexOf(listener);
-      if (idx != -1)
-        this._listeners.splice(idx, 1);
+      this._listeners.delete(listener);
     },
     _dispatch(...args)
     {
       let results = [];
-      let listeners = this._listeners.slice();
+      let listeners = [...this._listeners];

[Sebastian Noack, 2017/04/12 12:32:14]

Is turning the set into an array even necessary, can't you iterate over the set
directly below?

[Manish Jethani, 2017/04/12 12:37:50]

Yeah, I'm trying to be compatible with the current implementation. If a value is
removed from the set while you're iterating over it, it'll be skipped. It seems
we want to call all the listeners in the current iteration, even if the set is
modified.

https://hg.adblockplus.org/adblockpluschrome/rev/f81e41006b94

[Sebastian Noack, 2017/04/12 12:42:36]

I see. This might have been the reason why the list of listeners has been copied
in the first place.

[Wladimir Palant, 2017/04/12 14:43:02]

It is. However, is that an efficient way of copying a set? I can imagine new
Set(this._listeners) being considerably better.

[Sebastian Noack, 2017/04/12 14:49:30]

We don't need a set, an array is sufficient. So if [...] has performance issues
(I wouldn't know why it should), we should rather use Array.from(), I guess.

 
       for (let listener of listeners)
         results.push(listener(...args));