vue/src/platforms/web/runtime/modules/class.js

Reactive, component-oriented view layer for modern web interfaces.

/* @flow */

import { genClassForVnode, concat, stringifyClass } from 'web/util/index'

function updateClass (oldVnode: any, vnode: any) {
  const el = vnode.elm
  const data: VNodeData = vnode.data
  const oldData: VNodeData = oldVnode.data
  if (!data.staticClass && !data.class &&
      (!oldData || (!oldData.staticClass && !oldData.class))) {
    return
  }

  let cls = genClassForVnode(vnode)

  // handle transition classes
  const transitionClass = el._transitionClasses
  if (transitionClass) {
    cls = concat(cls, stringifyClass(transitionClass))
  }

  // set the class
  if (cls !== el._prevClass) {
    el.setAttribute('class', cls)
    el._prevClass = cls
  }
}

export default {
  create: updateClass,
  update: updateClass
}