Extend fast cases to multiple listeners.

Previously, only the case with 1 listener
was optimized for less than 3 event arguments.
This is now extended to any number of listeners.

Author: RubenVerborgh

lib/events.js

@@ -117,15 +117,30 @@ EventEmitter.prototype.emit = function emit(type, arg1, arg2) {
           args[i - 1] = arguments[i];
         handler.apply(this, args);
     }
-  } else if (util.isObject(handler)) {
-    args = new Array(len - 1);
-    for (i = 1; i < len; i++)
-      args[i - 1] = arguments[i];
-
+  } else if (util.isArray(handler)) {
     listeners = handler.slice();
-    len = listeners.length;
-    for (i = 0; i < len; i++)
-      listeners[i].apply(this, args);
+    switch (len) {
+      // fast cases
+      case 1:
+        for (i = 0, len = listeners.length; i < len; i++)
+          listeners[i].call(this);
+        break;
+      case 2:
+        for (i = 0, len = listeners.length; i < len; i++)
+          listeners[i].call(this, arg1);
+        break;
+      case 3:
+        for (i = 0, len = listeners.length; i < len; i++)
+          listeners[i].call(this, arg1, arg2);
+        break;
+      // slower
+      default:
+        args = new Array(len - 1);
+        for (i = 1; i < len; i++)
+          args[i - 1] = arguments[i];
+        for (i = 0, len = listeners.length; i < len; i++)
+          listeners[i].apply(this, args);
+    }
   }
 
   if (this.domain && this !== process)