Evented listener metadata now distinct per instance

src/event/Evented.js

@@ -20,10 +20,7 @@
  */
 
 var Trait   = require( 'easejs' ).Trait,
-    isArray = require( '../std/Array' ).isArray,
+    isArray = require( '../std/Array' ).isArray;
-
-    // used for hiding cached event indexes
-    _evid = Symbol();
 
 
 /**
@@ -55,6 +52,26 @@ module.exports = Trait( 'Evented',
      */
     _gaps: {},
 
+    /**
+     * Private listener metadata field
+     * @type {Symbol}
+     */
+    _evid: null,
+
+
+    /**
+     * Prepare private listener metadata field
+     *
+     * The event identifier field is set on registered listeners to provide
+     * constant-time lookups when querying for listener indexes or status.
+     *
+     * @O {1} constant time
+     */
+    __mixin()
+    {
+        this._evid = Symbol();
+    },
+
 
     /**
      * Defines a list of events by unique identifier
@@ -226,7 +243,8 @@ module.exports = Trait( 'Evented',
     'virtual protected hookEvent'( ev, listener )
     {
         let evls  = this._events[ ev ],
-            avail = this._gaps[ ev ].pop();
+            avail = this._gaps[ ev ].pop(),
+            _evid = this._evid;
 
         if ( listener[ _evid ] === undefined )
         {
@@ -262,7 +280,7 @@ module.exports = Trait( 'Evented',
      */
     hooksEvent( ev, listener )
     {
-        let levdata = listener[ _evid ];
+        let levdata = listener[ this._evid ];
         return !!( levdata && ( levdata[ ev ] !== undefined ) );
     },
 
@@ -307,7 +325,7 @@ module.exports = Trait( 'Evented',
         }
 
         let evls    = this._events[ ev ],
-            levdata = listener[ _evid ] || {},
+            levdata = listener[ this._evid ] || {},
             index   = levdata[ ev ];
 
         // this is important, since we (a) cannot necessarily trust that the

test/event/EventedTest.js

@@ -646,5 +646,28 @@ describe( 'event.Evented', () =>
             expect( stub.hooksEvent( ev2, f2 ) ).to.be.true;
         } );
     } );
+
+
+    describe( 'listener metadata', () =>
+    {
+        /**
+         * It is important that each Evented instance store its listener
+         * metadata in a distinct field; otherwise, they would query
+         * each-other, which would produce conflicts if the events happen to
+         * have the same name (which would not be uncommon).
+         */
+        it( 'is not accessible to other Evented instances', () =>
+        {
+            var ev = 'foo',
+                f  = () => {};
+
+            // this would fail if data were shared because the system would
+            // consider f to have already been registered with event `foo'
+            [ stub, EvStub() ].forEach( s =>
+                s.evDefineEvents( [ ev ] )
+                    .on( ev, f )
+            );
+        } );
+    } );
 } );