events: simplify removeAllListeners logic

Unnecessary checks were being performed on if the event existed before
being removed.

_events starts out as null, so reset to null when emptied.

Checking typeof is a lot cheaper than isArray().

lib/events.js

@@ -245,37 +245,42 @@ EventEmitter.prototype.removeListener = function(type, listener) {
 };
 
 EventEmitter.prototype.removeAllListeners = function(type) {
-  if (!this._events) return this;
+  var key, listeners;
 
-  // fast path
+  if (arguments.length > 0 && typeof type !== 'string')
+    throw TypeError('type must not be set or must be a string');
+
+  if (!this._events)
+    return this;
+
+  // not listening for removeListener, no need to emit
   if (!this._events.removeListener) {
-    if (arguments.length === 0) {
-      this._events = {};
-    } else if (type && this._events && this._events[type]) {
+    if (arguments.length === 0)
+      this._events = null;
+    else if (this._events[type])
       this._events[type] = null;
-    }
     return this;
   }
 
-  // slow(ish) path, emit 'removeListener' events for all removals
+  // emit removeListener for all listeners on all events
   if (arguments.length === 0) {
-    for (var key in this._events) {
+    for (key in this._events) {
       if (key === 'removeListener') continue;
       this.removeAllListeners(key);
     }
     this.removeAllListeners('removeListener');
-    this._events = {};
+    this._events = null;
     return this;
   }
 
-  var listeners = this._events[type];
-  if (isArray(listeners)) {
-    while (listeners.length) {
-      // LIFO order
-      this.removeListener(type, listeners[listeners.length - 1]);
-    }
-  } else if (listeners) {
+  listeners = this._events[type];
+
+  if (typeof listeners === 'function') {
     this.removeListener(type, listeners);
+  } else {
+    // LIFO order
+    while (listeners.length)
+      this.removeListener(type, listeners[listeners.length - 1]);
   }
   this._events[type] = null;