invokeCreateHooks

src/core/vdom/patch.js

  function invokeCreateHooks (vnode, insertedVnodeQueue) {
    // 这个cbs就是下面的cbs
    for (let i = 0; i < cbs.create.length; ++i) {
      // 这里就是modules中每个文件中的create方法,这里我就用class举例子了，看本文   *src/platforms/web/runtime/modules/class.js*中的create实现
      cbs.create[i](emptyNode, vnode)
    }
    i = vnode.data.hook // Reuse variable
    if (isDef(i)) {
      if (isDef(i.create)) i.create(emptyNode, vnode)
      if (isDef(i.insert)) insertedVnodeQueue.push(vnode)
    }
  }

src/core/vdom/patch.js

const hooks = ['create', 'activate', 'update', 'remove', 'destroy']

let i, j
const cbs = {}

const { modules, nodeOps } = backend

for (i = 0; i < hooks.length; ++i) {
  cbs[hooks[i]] = []
  for (j = 0; j < modules.length; ++j) {
    if (isDef(modules[j][hooks[i]])) {
      cbs[hooks[i]].push(modules[j][hooks[i]])
    }
  }
}

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

function updateClass (oldVnode: any, vnode: any) {
  const el = vnode.elm
  const data: VNodeData = vnode.data
  const oldData: VNodeData = oldVnode.data
  // 如果新老Vnode上没有直接返回
  if (
    isUndef(data.staticClass) &&
    isUndef(data.class) && (
      isUndef(oldData) || (
        isUndef(oldData.staticClass) &&
        isUndef(oldData.class)
      )
    )
  ) {
    return
  }
	// 这个就是新Vnode的class,这里会转成字符串
  let cls = genClassForVnode(vnode)

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

  //如果新老class不相等的就会用新的赋值，并且把_prevClass赋值
  if (cls !== el._prevClass) {
    el.setAttribute('class', cls)
    el._prevClass = cls
  }
}

export default {
  create: updateClass,
  update: updateClass
}

src/platforms/web/util/class.js

/* @flow */

import { isDef, isObject } from 'shared/util'

export function genClassForVnode (vnode: VNodeWithData): string {
  let data = vnode.data
  let parentNode = vnode
  let childNode = vnode
  while (isDef(childNode.componentInstance)) {
    childNode = childNode.componentInstance._vnode
    if (childNode && childNode.data) {
      data = mergeClassData(childNode.data, data)
    }
  }
  while (isDef(parentNode = parentNode.parent)) {
    if (parentNode && parentNode.data) {
      data = mergeClassData(data, parentNode.data)
    }
  }
  return renderClass(data.staticClass, data.class)
}

function mergeClassData (child: VNodeData, parent: VNodeData): {
  staticClass: string,
  class: any
} {
  return {
    staticClass: concat(child.staticClass, parent.staticClass),
    class: isDef(child.class)
      ? [child.class, parent.class]
      : parent.class
  }
}

export function renderClass (
  staticClass: ?string,
  dynamicClass: any
): string {
  if (isDef(staticClass) || isDef(dynamicClass)) {
    return concat(staticClass, stringifyClass(dynamicClass))
  }
  /* istanbul ignore next */
  return ''
}

export function concat (a: ?string, b: ?string): string {
  return a ? b ? (a + ' ' + b) : a : (b || '')
}

export function stringifyClass (value: any): string {
  if (Array.isArray(value)) {
    return stringifyArray(value)
  }
  if (isObject(value)) {
    return stringifyObject(value)
  }
  if (typeof value === 'string') {
    return value
  }
  /* istanbul ignore next */
  return ''
}

function stringifyArray (value: Array<any>): string {
  let res = ''
  let stringified
  for (let i = 0, l = value.length; i < l; i++) {
    if (isDef(stringified = stringifyClass(value[i])) && stringified !== '') {
      if (res) res += ' '
      res += stringified
    }
  }
  return res
}

function stringifyObject (value: Object): string {
  let res = ''
  for (const key in value) {
    if (value[key]) {
      if (res) res += ' '
      res += key
    }
  }
  return res
}