vue.js 源代码学习笔记 ----- instance render

/* @flow */

import {
  warn,
  nextTick,
  toNumber,
  _toString,
  looseEqual,
  emptyObject,
  handleError,
  looseIndexOf
} from '../util/index'

import VNode, {
  cloneVNodes,
  createTextVNode,
  createEmptyVNode
} from '../vdom/vnode'

import { createElement } from '../vdom/create-element'
import { renderList } from './render-helpers/render-list'
import { renderSlot } from './render-helpers/render-slot'
import { resolveFilter } from './render-helpers/resolve-filter'
import { checkKeyCodes } from './render-helpers/check-keycodes'
import { bindObjectProps } from './render-helpers/bind-object-props'
import { renderStatic, markOnce } from './render-helpers/render-static'
import { resolveSlots, resolveScopedSlots } from './render-helpers/resolve-slots'

export function initRender (vm: Component) {
  vm.$vnode = null // the placeholder node in parent tree 站位节点
  vm._vnode = null // the root of the child tree 根节点
  vm._staticTrees = null
  const parentVnode = vm.$options._parentVnode
  const renderContext = parentVnode && parentVnode.context
  vm.$slots = resolveSlots(vm.$options._renderChildren, renderContext)
  vm.$scopedSlots = emptyObject
  // bind the createElement fn to this instance
  // so that we get proper render context inside it.
  // args order: tag, data, children, normalizationType, alwaysNormalize
  // internal version is used by render functions compiled from templates
  // 把创建元素 的函数绑定到这个实例上, 这样就能得到合适的渲染上下文; 
  // 参数的顺序是: 标签 数据 子节点 规范化的类型 是否总是规范化
  vm._c = (a, b, c, d) => createElement(vm, a, b, c, d, false)
  // normalization is always applied for the public version, used in
  // user-written render functions.
  // 规范化总是应用在公共的版本, 应用在用户编写的 渲染函数
  vm.$createElement = (a, b, c, d) => createElement(vm, a, b, c, d, true)
}

export function renderMixin (Vue: Class<Component>) {
  //定义 $nextTick函数, 实际调用了 nextTick方法
  Vue.prototype.$nextTick = function (fn: Function) {
    return nextTick(fn, this)
  }

  Vue.prototype._render = function (): VNode {
    const vm: Component = this
    const {
      render,
      staticRenderFns,
      _parentVnode
    } = vm.$options

    if (vm._isMounted) {
      // clone slot nodes on re-renders
      for (const key in vm.$slots) {
       //克隆虚拟节点给自己
        vm.$slots[key] = cloneVNodes(vm.$slots[key])
      }
    }

   //scopedSlots ...
    vm.$scopedSlots = (_parentVnode && _parentVnode.data.scopedSlots) || emptyObject

    if (staticRenderFns && !vm._staticTrees) {
      vm._staticTrees = []
    }
    // set parent vnode. this allows render functions to have access
    // to the data on the placeholder node.
　　// 设置父虚拟节点, 这使得渲染函数可以访问站位节点上的数据

    vm.$vnode = _parentVnode
    // render self
    let vnode
    try {
      vnode = render.call(vm._renderProxy, vm.$createElement)
    } catch (e) {
      handleError(e, vm, `render function`)
      // return error render result,
      // or previous vnode to prevent render error causing blank component
      /* istanbul ignore else */
　　　　// 返回一个错误渲染的结果, 或者前一个虚拟节点放在呈现错误的时候引起空白组件
      if (process.env.NODE_ENV !== 'production') {
        vnode = vm.$options.renderError
          ? vm.$options.renderError.call(vm._renderProxy, vm.$createElement, e)
          : vm._vnode
      } else {
        vnode = vm._vnode
      }
    }
    // return empty vnode in case the render function errored out
    // 返回空的虚拟节点  假如渲染函数出错了
    if (!(vnode instanceof VNode)) {
      if (process.env.NODE_ENV !== 'production' && Array.isArray(vnode)) {
        warn(
          'Multiple root nodes returned from render function. Render function ' +
          'should return a single root node.',
          vm
        )
      }
      vnode = createEmptyVNode()
    }
    // set parent
    vnode.parent = _parentVnode
    return vnode
  }

  // internal render helpers.
  // these are exposed on the instance prototype to reduce generated render
  // code size.
  // 用简写, 生成实例的时候减少代码
  Vue.prototype._o = markOnce
  Vue.prototype._n = toNumber
  Vue.prototype._s = _toString
  Vue.prototype._l = renderList
  Vue.prototype._t = renderSlot
  Vue.prototype._q = looseEqual
  Vue.prototype._i = looseIndexOf
  Vue.prototype._m = renderStatic
  Vue.prototype._f = resolveFilter
  Vue.prototype._k = checkKeyCodes
  Vue.prototype._b = bindObjectProps
  Vue.prototype._v = createTextVNode
  Vue.prototype._e = createEmptyVNode
  Vue.prototype._u = resolveScopedSlots
}