events: _events to object and undefined not null

By making sure the _events is always an object there is one less check
that needs to be performed by emit.

Use undefined instead of null. typeof checks are a lot faster than
isArray.

There are a few places where the this._events check cannot be removed
because it is possible for the user to call those methods after using
utils.extend to create their own EventEmitter, but before it has
actually been instantiated.

lib/events.js

@@ -19,7 +19,6 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
 // USE OR OTHER DEALINGS IN THE SOFTWARE.
 
-var isArray = Array.isArray;
 var domain;
 
 exports.usingDomains = false;
@@ -33,7 +32,7 @@ function EventEmitter() {
       this.domain = domain.active;
     }
   }
-  this._events = this._events || null;
+  this._events = this._events || {};
   this._maxListeners = this._maxListeners || defaultMaxListeners;
 }
 exports.EventEmitter = EventEmitter;
@@ -57,8 +56,9 @@ var PROCESS;
 EventEmitter.prototype.emit = function(type) {
   // If there is no 'error' event listener then throw.
   if (type === 'error') {
-    if (!this._events || !this._events.error ||
+    if (!this._events.error ||
-        (isArray(this._events.error) && !this._events.error.length)) {
+        (typeof this._events.error === 'object' &&
+         !this._events.error.length)) {
       if (this.domain) {
         var er = arguments[1];
         er.domainEmitter = this;
@@ -77,7 +77,6 @@ EventEmitter.prototype.emit = function(type) {
     }
   }
 
-  if (!this._events) return false;
   var handler = this._events[type];
   if (!handler) return false;
 
@@ -111,7 +110,7 @@ EventEmitter.prototype.emit = function(type) {
     }
     return true;
 
-  } else if (isArray(handler)) {
+  } else if (typeof handler === 'object') {
     if (this.domain) {
       PROCESS = PROCESS || process;
       if (this !== PROCESS) {
@@ -153,7 +152,7 @@ EventEmitter.prototype.addListener = function(type, listener) {
   if (!this._events[type]) {
     // Optimize the case of one listener. Don't need the extra array object.
     this._events[type] = listener;
-  } else if (isArray(this._events[type])) {
+  } else if (typeof this._events[type] === 'object') {
 
     // If we've already got an array, just append.
     this._events[type].push(listener);
@@ -165,7 +164,7 @@ EventEmitter.prototype.addListener = function(type, listener) {
   }
 
   // Check for listener leak
-  if (isArray(this._events[type]) && !this._events[type].warned) {
+  if (typeof this._events[type] === 'object' && !this._events[type].warned) {
     var m;
     m = this._maxListeners;
 
@@ -219,11 +218,11 @@ EventEmitter.prototype.removeListener = function(type, listener) {
 
   if (list === listener ||
       (typeof list.listener === 'function' && list.listener === listener)) {
-    this._events[type] = null;
+    this._events[type] = undefined;
     if (this._events.removeListener)
       this.emit('removeListener', type, listener);
 
-  } else if (isArray(list)) {
+  } else if (typeof list === 'object') {
     for (i = 0; i < length; i++) {
       if (list[i] === listener ||
           (list[i].listener && list[i].listener === listener)) {
@@ -237,7 +236,7 @@ EventEmitter.prototype.removeListener = function(type, listener) {
 
     if (list.length === 1) {
       list.length = 0;
-      this._events[type] = null;
+      this._events[type] = undefined;
     } else {
       list.splice(position, 1);
     }
@@ -261,9 +260,9 @@ EventEmitter.prototype.removeAllListeners = function(type) {
   // not listening for removeListener, no need to emit
   if (!this._events.removeListener) {
     if (arguments.length === 0)
-      this._events = null;
+      this._events = {};
     else if (this._events[type])
-      this._events[type] = null;
+      this._events[type] = undefined;
     return this;
   }
 
@@ -274,7 +273,7 @@ EventEmitter.prototype.removeAllListeners = function(type) {
       this.removeAllListeners(key);
     }
     this.removeAllListeners('removeListener');
-    this._events = null;
+    this._events = {};
     return this;
   }
 
@@ -287,7 +286,7 @@ EventEmitter.prototype.removeAllListeners = function(type) {
     while (listeners.length)
       this.removeListener(type, listeners[listeners.length - 1]);
   }
-  this._events[type] = null;
+  this._events[type] = undefined;
 
   return this;
 };

src/node.cc

@@ -2477,6 +2477,9 @@ Handle<Object> SetupProcessObject(int argc, char *argv[]) {
                                                     3);
   process->Set(String::NewSymbol("_tickInfoBox"), info_box);
 
+  // pre-set _events object for faster emit checks
+  process->Set(String::NewSymbol("_events"), Object::New());
+
   return process;
 }
 

test/simple/test-event-emitter-listeners-side-effects.js

@@ -33,7 +33,7 @@ var fl;  // foo listeners
 fl = e.listeners('foo');
 assert(Array.isArray(fl));
 assert(fl.length === 0);
-assert.equal(e._events, null);
+assert.deepEqual(e._events, {});
 
 e.on('foo', assert.fail);
 fl = e.listeners('foo');

test/simple/test-event-emitter-set-max-listeners-side-effects.js

@@ -25,6 +25,6 @@ var events = require('events');
 
 var e = new events.EventEmitter;
 
-assert.strictEqual(e._events, null);
+assert.deepEqual(e._events, {});
 e.setMaxListeners(5);
-assert.strictEqual(e._events, null);
+assert.deepEqual(e._events, {});