helperify core vdom helpers

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

@@ -1,7 +1,7 @@
 /* @flow */
 
-import { remove } from 'shared/util'
 import { createFnInvoker } from './update-listeners'
+import { remove, isDef, isUndef, isTrue } from 'shared/util'
 
 export function mergeVNodeHook (def: Object, hookKey: string, hook: Function) {
   let invoker
@@ -14,12 +14,12 @@ export function mergeVNodeHook (def: Object, hookKey: string, hook: Function) {
     remove(invoker.fns, wrappedHook)
   }
 
-  if (!oldHook) {
+  if (isUndef(oldHook)) {
     // no existing hook
     invoker = createFnInvoker([wrappedHook])
   } else {
     /* istanbul ignore if */
-    if (oldHook.fns && oldHook.merged) {
+    if (isDef(oldHook.fns) && isTrue(oldHook.merged)) {
       // already a merged invoker
       invoker = oldHook
       invoker.fns.push(wrappedHook)

src/core/vdom/helpers/normalize-children.js

@@ -1,7 +1,7 @@
 /* @flow */
 
-import { isPrimitive } from 'core/util/index'
 import VNode, { createTextVNode } from 'core/vdom/vnode'
+import { isDef, isUndef, isPrimitive } from 'shared/util'
 
 // The template compiler attempts to minimize the need for normalization by
 // statically analyzing the template at compile time.
@@ -41,25 +41,25 @@ function normalizeArrayChildren (children: any, nestedIndex?: string): Array<VNo
   let i, c, last
   for (i = 0; i < children.length; i++) {
     c = children[i]
-    if (c == null || typeof c === 'boolean') continue
+    if (isUndef(c) || typeof c === 'boolean') continue
     last = res[res.length - 1]
     //  nested
     if (Array.isArray(c)) {
       res.push.apply(res, normalizeArrayChildren(c, `${nestedIndex || ''}_${i}`))
     } else if (isPrimitive(c)) {
-      if (last && last.text) {
-        last.text += String(c)
+      if (isDef(last) && isDef(last.text)) {
+        (last: any).text += String(c)
       } else if (c !== '') {
         // convert primitive to vnode
         res.push(createTextVNode(c))
       }
     } else {
-      if (c.text && last && last.text) {
+      if (isDef(c.text) && isDef(last) && isDef(last.text)) {
         res[res.length - 1] = createTextVNode(last.text + c.text)
       } else {
         // default key for nested array children (likely generated by v-for)
-        if (c.tag && c.key == null && nestedIndex != null) {
-          c.key = `__vlist${nestedIndex}_${i}__`
+        if (isDef(c.tag) && isUndef(c.key) && isDef(nestedIndex)) {
+          c.key = `__vlist${(nestedIndex: any)}_${i}__`
         }
         res.push(c)
       }

src/core/vdom/helpers/update-listeners.js

@@ -1,7 +1,7 @@
 /* @flow */
 
-import { cached } from 'shared/util'
 import { warn } from 'core/util/index'
+import { cached, isUndef } from 'shared/util'
 
 const normalizeEvent = cached((name: string): {
   name: string,
@@ -51,13 +51,13 @@ export function updateListeners (
     cur = on[name]
     old = oldOn[name]
     event = normalizeEvent(name)
-    if (!cur) {
+    if (isUndef(cur)) {
       process.env.NODE_ENV !== 'production' && warn(
         `Invalid handler for event "${event.name}": got ` + String(cur),
         vm
       )
-    } else if (!old) {
-      if (!cur.fns) {
+    } else if (isUndef(old)) {
+      if (isUndef(cur.fns)) {
         cur = on[name] = createFnInvoker(cur)
       }
       add(event.name, cur, event.once, event.capture, event.passive)
@@ -67,7 +67,7 @@ export function updateListeners (
     }
   }
   for (name in oldOn) {
-    if (!on[name]) {
+    if (isUndef(on[name])) {
       event = normalizeEvent(name)
       remove(event.name, oldOn[name], event.capture)
     }