optimize instance hook event lookup

Author: yyx990803

flow/component.js

@@ -64,6 +64,7 @@ declare interface Component {
   _isBeingDestroyed: boolean;
   _vnode: ?VNode;
   _staticTrees: ?Array<VNode>;
+  _hasHookEvent: boolean;
 
   // private methods
   // lifecycle

src/core/instance/events.js

@@ -5,6 +5,7 @@ import { updateListeners } from '../vdom/helpers/index'
 
 export function initEvents (vm: Component) {
   vm._events = Object.create(null)
+  vm._hasHookEvent = false
   // init parent attached events
   const listeners = vm.$options._parentListeners
   if (listeners) {
@@ -36,9 +37,15 @@ export function updateComponentListeners (
 }
 
 export function eventsMixin (Vue: Class<Component>) {
+  const hookRE = /^hook:/
   Vue.prototype.$on = function (event: string, fn: Function): Component {
     const vm: Component = this
     ;(vm._events[event] || (vm._events[event] = [])).push(fn)
+    // optimize hook:event cost by using a boolean flag marked at registration
+    // instead of a hash lookup
+    if (hookRE.test(event)) {
+      vm._hasHookEvent = true
+    }
     return vm
   }
 
@@ -87,7 +94,7 @@ export function eventsMixin (Vue: Class<Component>) {
     let cbs = vm._events[event]
     if (cbs) {
       cbs = cbs.length > 1 ? toArray(cbs) : cbs
-      const args = arguments.length > 1 ? toArray(arguments, 1) : void 0
+      const args = toArray(arguments, 1)
       for (let i = 0, l = cbs.length; i < l; i++) {
         cbs[i].apply(vm, args)
       }

src/core/instance/lifecycle.js

@@ -211,5 +211,7 @@ export function callHook (vm: Component, hook: string) {
       handlers[i].call(vm)
     }
   }
-  vm.$emit('hook:' + hook)
+  if (vm._hasHookEvent) {
+    vm.$emit('hook:' + hook)
+  }
 }