events: removeListener add checks and cleanup

Remove unecessary splice for single listener events. Add type check for
"type" argument.

lib/events.js

@@ -203,43 +203,48 @@ EventEmitter.prototype.once = function(type, listener) {
 
 // emits a 'removeListener' event iff the listener was removed
 EventEmitter.prototype.removeListener = function(type, listener) {
-  if ('function' !== typeof listener) {
-    throw TypeError('removeListener only takes instances of Function');
-  }
+  var list, position, length, i;
 
-  // does not use listeners(), so no side effect of creating _events[type]
-  if (!this._events || !this._events[type]) return this;
+  if (typeof type !== 'string')
+    throw TypeError('type must be a string');
+  if (typeof listener !== 'function')
+    throw TypeError('listener must be a function');
 
-  var list = this._events[type];
+  if (!this._events || !this._events[type])
+    return this;
+
+  list = this._events[type];
+  length = list.length;
+  position = -1;
+
+  if (list === listener ||
+      (typeof list.listener === 'function' && list.listener === listener)) {
+    this._events[type] = null;
+    if (this._events.removeListener)
+      this.emit('removeListener', type, listener);
 
-  if (isArray(list)) {
-    var position = -1;
-    for (var i = 0, length = list.length; i < length; i++) {
+  } else if (isArray(list)) {
+    for (i = 0; i < length; i++) {
       if (list[i] === listener ||
-          (list[i].listener && list[i].listener === listener))
-      {
+          (list[i].listener && list[i].listener === listener)) {
         position = i;
         break;
       }
     }
 
-    if (position < 0) return this;
-    list.splice(position, 1);
-    if (list.length == 0)
-      this._events[type] = null;
+    if (position < 0)
+      return this;
 
-    if (this._events.removeListener) {
-      this.emit('removeListener', type, listener);
-    }
-  } else if (list === listener ||
-             (list.listener && list.listener === listener))
-  {
+    if (list.length === 1) {
+      list.length = 0;
       this._events[type] = null;
+    } else {
+      list.splice(position, 1);
+    }
 
-    if (this._events.removeListener) {
+    if (this._events.removeListener)
       this.emit('removeListener', type, listener);
   }
-  }
 
   return this;
 };