refactor: simplify mergeVNodeHook usage

src/core/vdom/helpers/merge-hook.js

@@ -1,9 +1,13 @@
 /* @flow */
 
+import VNode from '../vnode'
 import { createFnInvoker } from './update-listeners'
 import { remove, isDef, isUndef, isTrue } from 'shared/util'
 
 export function mergeVNodeHook (def: Object, hookKey: string, hook: Function) {
+  if (def instanceof VNode) {
+    def = def.data.hook || (def.data.hook = {})
+  }
   let invoker
   const oldHook = def[hookKey]
 

src/core/vdom/modules/directives.js

@@ -54,14 +54,14 @@ function _update (oldVnode, vnode) {
       }
     }
     if (isCreate) {
-      mergeVNodeHook(vnode.data.hook || (vnode.data.hook = {}), 'insert', callInsert)
+      mergeVNodeHook(vnode, 'insert', callInsert)
     } else {
       callInsert()
     }
   }
 
   if (dirsWithPostpatch.length) {
-    mergeVNodeHook(vnode.data.hook || (vnode.data.hook = {}), 'postpatch', () => {
+    mergeVNodeHook(vnode, 'postpatch', () => {
       for (let i = 0; i < dirsWithPostpatch.length; i++) {
         callHook(dirsWithPostpatch[i], 'componentUpdated', vnode, oldVnode)
       }

src/platforms/web/runtime/directives/model.js

@@ -24,7 +24,7 @@ const directive = {
     if (vnode.tag === 'select') {
       // #6903
       if (oldVnode.elm && !oldVnode.elm._vOptions) {
-        mergeVNodeHook(vnode.data.hook || (vnode.data.hook = {}), 'postpatch', () => {
+        mergeVNodeHook(vnode, 'postpatch', () => {
           directive.componentUpdated(el, binding, vnode)
         })
       } else {

src/platforms/web/runtime/modules/transition.js

@@ -130,7 +130,7 @@ export function enter (vnode: VNodeWithData, toggleDisplay: ?() => void) {
 
   if (!vnode.data.show) {
     // remove pending leave element on enter by injecting an insert hook
-    mergeVNodeHook(vnode.data.hook || (vnode.data.hook = {}), 'insert', () => {
+    mergeVNodeHook(vnode, 'insert', () => {
       const parent = el.parentNode
       const pendingNode = parent && parent._pending && parent._pending[vnode.key]
       if (pendingNode &&