events: add check for listeners length

Ability to return just the length of listeners for a given type, using
EventEmitter.listenerCount(emitter, event). This will be a lot cheaper
than creating a copy of the listeners array just to check its length.

1 files changed, 11 insertions, 0 deletions

diff --git a/lib/events.js b/lib/events.js
index 223015ec6..69af3aee6 100644
--- a/lib/events.js
+++ b/lib/events.js
@@ -286,3 +286,14 @@ EventEmitter.prototype.listeners = function(type) {
   }
   return this._events[type].slice(0);
 };
+
+EventEmitter.listenerCount = function(emitter, type) {
+  var ret;
+  if (!emitter._events || !emitter._events[type])
+    ret = 0;
+  else if (typeof emitter._events[type] === 'function')
+    ret = 1;
+  else
+    ret = emitter._events[type].length;
+  return ret;
+};