Avoid memory leaks by remove event arrays

When subscribing and then unsubscribing from many different types of events,
it can be observed that the `Emitter._callbacks` object starts to grow.
This happens because, when unsubscribing, the event specific event array
is not removed when the last subscriber unsubscribes.

index.js

@@ -109,6 +109,13 @@ Emitter.prototype.removeEventListener = function(event, fn){
  break;
  }
  }
+
+ // Remove event specific arrays for event types that no
+ // one is subscribed for to avoid memory leak.
+ if (callbacks.length === 0) {
+ delete this._callbacks['$' + event];
+ }
+
  return this;
 };
 

test/emitter.js

@@ -142,6 +142,32 @@ describe('Emitter', function(){
 
  calls.should.eql([]);
  })
+
+ it('should remove event array to avoid memory leak', function() {
+ var emitter = new Emitter;
+ var calls = [];
+
+ function cb() {}
+
+ emitter.on('foo', cb);
+ emitter.off('foo', cb);
+
+ emitter._callbacks.should.not.have.property('$foo');
+ })
+
+ it('should only remove the event array when the last subscriber unsubscribes', function() {
+ var emitter = new Emitter;
+ var calls = [];
+
+ function cb1() {}
+ function cb2() {}
+
+ emitter.on('foo', cb1);
+ emitter.on('foo', cb2);
+ emitter.off('foo', cb1);
+
+ emitter._callbacks.should.have.property('$foo');
+ })
  })
 
  describe('.off()', function(){