early return in vdom update modules

src/runtime/dom-backend/modules/attrs.js

@@ -14,6 +14,9 @@ const xlinkNS = 'http://www.w3.org/1999/xlink'
 const isXlink = name => name.slice(0, 6) === 'xlink:'
 
 function updateAttrs (oldVnode, vnode) {
+  if (!oldVnode.data.attrs && !vnode.data.attrs) {
+    return
+  }
   let key, cur, old
   const elm = vnode.elm
   const oldAttrs = oldVnode.data.attrs || {}

src/runtime/dom-backend/modules/events.js

@@ -1,6 +1,9 @@
 import { updateListeners } from '../../vdom/helpers'
 
 function updateDOMListeners (oldVnode, vnode) {
+  if (!oldVnode.data.on && !vnode.data.on) {
+    return
+  }
   const on = vnode.data.on
   const oldOn = oldVnode.data.on || {}
   updateListeners(on, oldOn, (event, handler, capture) => {

src/runtime/dom-backend/modules/props.js

@@ -1,4 +1,7 @@
 function updateProps (oldVnode, vnode) {
+  if (!oldVnode.data.props && !vnode.data.props) {
+    return
+  }
   let key, cur, old
   const elm = vnode.elm
   const oldProps = oldVnode.data.props || {}

src/runtime/dom-backend/modules/style.js

@@ -29,6 +29,9 @@ function toObject (arr) {
 }
 
 function updateStyle (oldVnode, vnode) {
+  if (!oldVnode.data.style && !vnode.data.style) {
+    return
+  }
   let cur, name
   const elm = vnode.elm
   const oldStyle = oldVnode.data.style || {}