use fn.apply in external vm event methods

Author: Evan You

src/emitter.js

@@ -1,17 +1,19 @@
+var slice = [].slice
+
 function Emitter (ctx) {
     this._ctx = ctx || this
 }
 
 var EmitterProto = Emitter.prototype
 
-EmitterProto.on = function(event, fn){
+EmitterProto.on = function (event, fn) {
     this._cbs = this._cbs || {}
     ;(this._cbs[event] = this._cbs[event] || [])
         .push(fn)
     return this
 }
 
-EmitterProto.once = function(event, fn){
+EmitterProto.once = function (event, fn) {
     var self = this
     this._cbs = this._cbs || {}
 
@@ -25,7 +27,7 @@ EmitterProto.once = function(event, fn){
     return this
 }
 
-EmitterProto.off = function(event, fn){
+EmitterProto.off = function (event, fn) {
     this._cbs = this._cbs || {}
 
     // all
@@ -56,7 +58,11 @@ EmitterProto.off = function(event, fn){
     return this
 }
 
-EmitterProto.emit = function(event, a, b, c){
+/**
+ *  The internal, faster emit with fixed amount of arguments
+ *  using Function.call
+ */
+EmitterProto.emit = function (event, a, b, c) {
     this._cbs = this._cbs || {}
     var callbacks = this._cbs[event]
 
@@ -70,4 +76,22 @@ EmitterProto.emit = function(event, a, b, c){
     return this
 }
 
+/**
+ *  The external emit using Function.apply
+ */
+EmitterProto.applyEmit = function (event) {
+    this._cbs = this._cbs || {}
+    var callbacks = this._cbs[event], args
+
+    if (callbacks) {
+        callbacks = callbacks.slice(0)
+        args = slice.call(arguments, 1)
+        for (var i = 0, len = callbacks.length; i < len; i++) {
+            callbacks[i].apply(this._ctx, args)
+        }
+    }
+
+    return this
+}
+
 module.exports = Emitter

src/viewmodel.js

@@ -94,7 +94,7 @@ def(VMProto, '$broadcast', function () {
         child
     while (i--) {
         child = children[i]
-        child.emitter.emit.apply(child.emitter, arguments)
+        child.emitter.applyEmit.apply(child.emitter, arguments)
         child.vm.$broadcast.apply(child.vm, arguments)
     }
 })
@@ -106,7 +106,7 @@ def(VMProto, '$dispatch', function () {
     var compiler = this.$compiler,
         emitter = compiler.emitter,
         parent = compiler.parent
-    emitter.emit.apply(emitter, arguments)
+    emitter.applyEmit.apply(emitter, arguments)
     if (parent) {
         parent.vm.$dispatch.apply(parent.vm, arguments)
     }
@@ -116,9 +116,15 @@ def(VMProto, '$dispatch', function () {
  *  delegate on/off/once to the compiler's emitter
  */
 ;['emit', 'on', 'off', 'once'].forEach(function (method) {
+    // internal emit has fixed number of arguments.
+    // exposed emit uses the external version
+    // with fn.apply.
+    var realMethod = method === 'emit'
+        ? 'applyEmit'
+        : method
     def(VMProto, '$' + method, function () {
         var emitter = this.$compiler.emitter
-        emitter[method].apply(emitter, arguments)
+        emitter[realMethod].apply(emitter, arguments)
     })
 })