text: /* @flow */
  
  import {
      isUndef
  } from 'shared/util'
  
  import {
      genClassStyleForVnode,
      updateElemStyle
  } from 'weex/util/class'
  
  function updateClass(oldVnode: VNodeWithData, vnode: VNodeWithData) {
      const data: VNodeData = vnode.data
      const oldData: VNodeData = oldVnode.data
      if (
          isUndef(data.staticClass) &&
          isUndef(data.class) && (
              isUndef(oldData) || (
                  isUndef(oldData.staticClass) &&
                  isUndef(oldData.class)
              )
          )
      ) {
          return
      }
  
      updateElemStyle(
          vnode.elm,
          genClassStyleForVnode(vnode),
          genClassStyleForVnode(oldVnode),
          normalize
      )
  }
  
  function normalize(name) { //class 已在编译阶段处理
      return name
  }
  
  export default {
      create: updateClass,
      update: updateClass
  }
  