Vue源码解析二(render&mount)

冷不防 2022-04-04 14:54 246阅读 0赞

**前言:前面我们根据vue官网的生命周期图走了一遍vue的源码,感兴趣的小伙伴可以去看我之前的文章[Vue源码解析(一)][Vue],今天我们重点研究一下render跟mount方法,这也是vue中两个比较重要的方法了,废话不多说了,我们开撸~~**

我们先回顾下上节内容,我们打开vue的源码,然后找到/vue/src/core/instance/init.js:

Vue.prototype._init = function (options?: Object) {
        const vm: Component = this
        // a uid
        vm._uid = uid++
    
        let startTag, endTag
        /* istanbul ignore if */
        if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
          startTag = `vue-perf-start:${vm._uid}`
          endTag = `vue-perf-end:${vm._uid}`
          mark(startTag)
        }
    
        // a flag to avoid this being observed
        vm._isVue = true
        // merge options
        if (options && options._isComponent) {
          // optimize internal component instantiation
          // since dynamic options merging is pretty slow, and none of the
          // internal component options needs special treatment.
          initInternalComponent(vm, options)
        } else {
          vm.$options = mergeOptions(
            resolveConstructorOptions(vm.constructor),
            options || {},
            vm
          )
        }
        /* istanbul ignore else */
        if (process.env.NODE_ENV !== 'production') {
          initProxy(vm)
        } else {
          vm._renderProxy = vm
        }
        // expose real self
        vm._self = vm
        initLifecycle(vm)
        initEvents(vm)
        initRender(vm)
        callHook(vm, 'beforeCreate')
        initInjections(vm) // resolve injections before data/props
        initState(vm)
        initProvide(vm) // resolve provide after data/props
        callHook(vm, 'created')
    
        /* istanbul ignore if */
        if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
          vm._name = formatComponentName(vm, false)
          mark(endTag)
          measure(`vue ${vm._name} init`, startTag, endTag)
        }
    
        if (vm.$options.el) {
          vm.$mount(vm.$options.el)
        }
      }

可以说这段代码就是贯穿了vue的整个生命周期,我们可以看到最后一行代码:

if (vm.$options.el) {
          vm.$mount(vm.$options.el)
        }

当我们的vue实例中有el属性的时候就会直接走vm的mount方法,那么如果我们不提供el属性的时候,我们该怎么走呢?

我们创建一个简单的vue页面:

page-a.vue:

<template>
      <div id="page-a-container">
        <button @click="onClick">登录</button>
      </div>
    </template>
    <script>
      import Render3 from '../components/Render3'
      export default {
        name: 'pageA',
        mounted() {
        },
        methods: {
          onClick() {
            this.$store.dispatch('login')
          }
        }
      }
    </script>
    <style scoped>
      #page-a-container {
        color: white;
        font-size: 24px;
        height: 100%;
      }
    </style>

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3Z2X2J1Zw_size_16_color_FFFFFF_t_70]

然后我们在page-a.vue中引用一个叫Render3.js的组件:

export default {
      name: 'Render3',
      render() {
        return <div>我是render3</div>
      }
    }

可以看到,我们直接用js文件定义了一个对象,对象里面有name属性跟render方法,render方法我们待会再分析,那么我们怎么才能page-a.vue中用起来呢?

方法一:

mounted() {
     	//继承vue的属性
          let Render3Class=this.$options._base.extend(Render3)
          //创建一个vue实例
          let render3VM=new Render3Class({
          //创建一个空元素
            el: document.createElement('div')
          })
          //把render3VM的el添加到当前vue的el中
          this.$el.appendChild(render3VM.$el)
        },

然后我们运行代码:  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3Z2X2J1Zw_size_16_color_FFFFFF_t_70 1]

我们还可以直接把组件注册为局部组件或者全局组件:

<template>
      <div id="page-a-container">
        <button @click="onClick">登录</button>
        <render3></render3>
      </div>
    </template>
    <script>
      import Render3 from '../components/Render3'
      export default {
        name: 'pageA',
        mounted() {
    //      let Render3Class=this.$options._base.extend(Render3)
    //      let render3VM=new Render3Class({
    //        el: document.createElement('div')
    //      })
    //      this.$el.appendChild(render3VM.$el)
        },
        methods: {
          onClick() {
            this.$store.dispatch('login')
          }
        },
        components:{
          Render3
        }
      }
    </script>
    <style scoped>
      #page-a-container {
        font-size: 24px;
        height: 100%;
      }
    </style>

第二种我就不介绍了哈,小伙伴都会用,我们看一下第一种方式:

import Render3 from '../components/Render3'
      export default {
        name: 'pageA',
        mounted() {
          let Render3Class=this.$options._base.extend(Render3)
          let render3VM=new Render3Class({
            el: document.createElement('div')
          })
          this.$el.appendChild(render3VM.$el)
        },
        methods: {
          onClick() {
            this.$store.dispatch('login')
          }
        }

我们前面知道,当提供了el属性给vm的时候,直接会走mount方法,我们把el属性注释掉试试:

mounted() {
          let Render3Class=this.$options._base.extend(Render3)
          let render3VM=new Render3Class({
    //        el: document.createElement('div')
          })
          this.$el.appendChild(render3VM.$el)
        },

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3Z2X2J1Zw_size_16_color_FFFFFF_t_70 2]

可以看到,render3没有被渲染,那我们怎么办呢? 我们可以自己调用一下:

mounted() {
          let Render3Class=this.$options._base.extend(Render3)
          let render3VM=new Render3Class({
    //        el: document.createElement('div')
          })
          render3VM.$mount(document.createElement('div'))
          this.$el.appendChild(render3VM.$el)
        },

我就不截图了哈,效果跟之前一样,我们来分析一下mount方法,mount方法字面上意思就是“渲染”的意思,当我们直接执行:

render3VM.$mount(document.createElement('div'))

方法的时候,我们首先走了/vue/src/platforms/web/entry-runtime-with-compiler.js:

const mount = Vue.prototype.$mount
    Vue.prototype.$mount = function (
      el?: string | Element,
      hydrating?: boolean
    ): Component {
      //在vm中传递的el属性
      el = el && query(el)
    
      /* istanbul ignore if */
      if (el === document.body || el === document.documentElement) {
        process.env.NODE_ENV !== 'production' && warn(
          `Do not mount Vue to <html> or <body> - mount to normal elements instead.`
        )
        return this
      }
    
      const options = this.$options
      // 如果在options中没有传递render方法
      if (!options.render) {
        let template = options.template
        //如果有template属性，就把template编译完毕后传递给render方法
        if (template) {
          if (typeof template === 'string') {
            if (template.charAt(0) === '#') {
              template = idToTemplate(template)
              /* istanbul ignore if */
              if (process.env.NODE_ENV !== 'production' && !template) {
                warn(
                  `Template element not found or is empty: ${options.template}`,
                  this
                )
              }
            }
          } else if (template.nodeType) {
            template = template.innerHTML
          } else {
            if (process.env.NODE_ENV !== 'production') {
              warn('invalid template option:' + template, this)
            }
            return this
          }
        } else if (el) {
          //如果没有template属性但是有el属性的时候，把el的outerHtml当成template传递给render对象
          template = getOuterHTML(el)
        }
        if (template) {
          /* istanbul ignore if */
          if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
            mark('compile')
          }
    
          const { render, staticRenderFns } = compileToFunctions(template, {
            shouldDecodeNewlines,
            shouldDecodeNewlinesForHref,
            delimiters: options.delimiters,
            comments: options.comments
          }, this)
          options.render = render
          options.staticRenderFns = staticRenderFns
    
          /* istanbul ignore if */
          if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
            mark('compile end')
            measure(`vue ${this._name} compile`, 'compile', 'compile end')
          }
        }
      }
      return mount.call(this, el, hydrating)
    }

然后会走vue/src/platforms/web/runtime/index.js:

Vue.prototype.$mount = function (
      el?: string | Element,
      hydrating?: boolean
    ): Component {
      el = el && inBrowser ? query(el) : undefined
      return mountComponent(this, el, hydrating)
    }

最后会走vue/src/core/instance/lifecycle.js:

export function mountComponent (
      vm: Component,
      el: ?Element,
      hydrating?: boolean
    ): Component {
      vm.$el = el
      if (!vm.$options.render) {
        vm.$options.render = createEmptyVNode
        if (process.env.NODE_ENV !== 'production') {
          /* istanbul ignore if */
          if ((vm.$options.template && vm.$options.template.charAt(0) !== '#') ||
            vm.$options.el || el) {
            warn(
              'You are using the runtime-only build of Vue where the template ' +
              'compiler is not available. Either pre-compile the templates into ' +
              'render functions, or use the compiler-included build.',
              vm
            )
          } else {
            warn(
              'Failed to mount component: template or render function not defined.',
              vm
            )
          }
        }
      }
      callHook(vm, 'beforeMount')
    
      let updateComponent
      /* istanbul ignore if */
      if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
        updateComponent = () => {
          const name = vm._name
          const id = vm._uid
          const startTag = `vue-perf-start:${id}`
          const endTag = `vue-perf-end:${id}`
    
          mark(startTag)
          const vnode = vm._render()
          mark(endTag)
          measure(`vue ${name} render`, startTag, endTag)
    
          mark(startTag)
          vm._update(vnode, hydrating)
          mark(endTag)
          measure(`vue ${name} patch`, startTag, endTag)
        }
      } else {
        updateComponent = () => {
          vm._update(vm._render(), hydrating)
        }
      }
    
      // we set this to vm._watcher inside the watcher's constructor
      // since the watcher's initial patch may call $forceUpdate (e.g. inside child
      // component's mounted hook), which relies on vm._watcher being already defined
      new Watcher(vm, updateComponent, noop, null, true /* isRenderWatcher */)
      hydrating = false
    
      // manually mounted instance, call mounted on self
      // mounted is called for render-created child components in its inserted hook
      if (vm.$vnode == null) {
        vm._isMounted = true
        callHook(vm, 'mounted')
      }
      return vm

可以看到,最后执行了回调了mounted事件,我们组件中的mounted方法被执行,在第一行中我们可以看到:

vm.$el = el

所以也是为什么我们在beforecreated跟created方法中拿不到this. e l 的 原 因 , 因 为 t h i s . el的原因,因为this. el的原因,因为this.el还没被赋值.

mount方法的整个流程我们简单的走了一遍了,我们再反过来一起研究一下render方法,render基本用法我就不解释了,官网比我说的好,小伙伴可以自己看官网哈,  
[https://cn.vuejs.org/v2/guide/render-function.html][https_cn.vuejs.org_v2_guide_render-function.html]

**我们重点研究一下render方法的源码**

小伙伴有没有发现,在vue文件中如果提供了render方法,render方法不执行?

这其实跟vue-loader有关,当vue-loader在加载.vue文件的时候,当发现.vue文件中有template标签的时候,就会把template解析完毕后然后创建render方法,替换当前vm的render方法,所以我们在.vue文件中提供的render方法其实是被覆盖掉了,所以如果在.vue文件中使用render方法的时候,我们需要去掉template标签.

像这样的:

vue-loader的源码我这就不解析了,不然写不完了,哈哈~~  
好啦,又说了一段废话,我们还是快进入我们的主题哈

我们继续看这个文件中的mount方法vue/src/platforms/web/entry-runtime-with-compiler.js:

Vue.prototype.$mount = function (
      el?: string | Element,
      hydrating?: boolean
    ): Component {
      //在vm中传递的el属性
      el = el && query(el)
    
      /* istanbul ignore if */
      if (el === document.body || el === document.documentElement) {
        process.env.NODE_ENV !== 'production' && warn(
          `Do not mount Vue to <html> or <body> - mount to normal elements instead.`
        )
        return this
      }
    
      const options = this.$options
      // 如果在options中没有传递render方法
      if (!options.render) {
        let template = options.template
        //如果有template属性，就把template编译完毕后传递给render方法
        if (template) {
          if (typeof template === 'string') {
            if (template.charAt(0) === '#') {
              template = idToTemplate(template)
              /* istanbul ignore if */
              if (process.env.NODE_ENV !== 'production' && !template) {
                warn(
                  `Template element not found or is empty: ${options.template}`,
                  this
                )
              }
            }
          } else if (template.nodeType) {
            template = template.innerHTML
          } else {
            if (process.env.NODE_ENV !== 'production') {
              warn('invalid template option:' + template, this)
            }
            return this
          }
        } else if (el) {
          //如果没有template属性但是有el属性的时候，把el的outerHtml当成template传递给render对象
          template = getOuterHTML(el)
        }
        if (template) {
          /* istanbul ignore if */
          if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
            mark('compile')
          }
    
          const { render, staticRenderFns } = compileToFunctions(template, {
            shouldDecodeNewlines,
            shouldDecodeNewlinesForHref,
            delimiters: options.delimiters,
            comments: options.comments
          }, this)
          options.render = render
          options.staticRenderFns = staticRenderFns
    
          /* istanbul ignore if */
          if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
            mark('compile end')
            measure(`vue ${this._name} compile`, 'compile', 'compile end')
          }
        }
      }
      return mount.call(this, el, hydrating)
    }

我们刚也说了,当.vue文件的时候vue-loader会判断template标签,然后创建render方法,所以我们在这的时候默认认为是有render方法的,那如果.vue中没有template标签也没有提供render方法的话该怎么走呢?

在mountComponent方法中我们看到,如果我们没有提供render方法的时候,vue就会自动给我们创建一个空的vnode对象:

vm.$options.render = createEmptyVNode

export const createEmptyVNode = (text: string = '') => {
      const node = new VNode()
      node.text = text
      node.isComment = true
      return node
    }

我们还是继续回到这个文件哈  
/vue/src/platforms/web/entry-runtime-with-compiler.js:

if (!options.render) {
        let template = options.template
        //如果有template属性，就把template编译完毕后传递给render方法
        if (template) {
          if (typeof template === 'string') {
            if (template.charAt(0) === '#') {
              template = idToTemplate(template)
              /* istanbul ignore if */
              if (process.env.NODE_ENV !== 'production' && !template) {
                warn(
                  `Template element not found or is empty: ${options.template}`,
                  this
                )
              }
            }
          } else if (template.nodeType) {
            template = template.innerHTML
          } else {
            if (process.env.NODE_ENV !== 'production') {
              warn('invalid template option:' + template, this)
            }
            return this
          }
        } else if (el) {
          //如果没有template属性但是有el属性的时候，把el的outerHtml当成template传递给render对象
          template = getOuterHTML(el)
        }
        if (template) {
          /* istanbul ignore if */
          if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
            mark('compile')
          }
    
          const { render, staticRenderFns } = compileToFunctions(template, {
            shouldDecodeNewlines,
            shouldDecodeNewlinesForHref,
            delimiters: options.delimiters,
            comments: options.comments
          }, this)
          options.render = render
          options.staticRenderFns = staticRenderFns
    
          /* istanbul ignore if */
          if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
            mark('compile end')
            measure(`vue ${this._name} compile`, 'compile', 'compile end')
          }
        }

当判断有template的时候,我们就走了下面代码:

if (template) {
         ...
          const { render, staticRenderFns } = compileToFunctions(template, {
            shouldDecodeNewlines,
            shouldDecodeNewlinesForHref,
            delimiters: options.delimiters,
            comments: options.comments
          }, this)
          options.render = render
          options.staticRenderFns = staticRenderFns
    
         ....
        }

我们可以看到当有template的时候,我们走了compileToFunctions方法,然后生成了render方法,我们看一下compileToFunctions方法,vue/src/platforms/web/compiler/index.js:

import { baseOptions } from './options'
    import { createCompiler } from 'compiler/index'
    
    const { compile, compileToFunctions } = createCompiler(baseOptions)
    
    export { compile, compileToFunctions }

然后compileToFunctions方法我们可以看到在这定义的  
vue/src/compiler/index.js:

export const createCompiler = createCompilerCreator(function baseCompile (
      template: string,
      options: CompilerOptions
    ): CompiledResult {
      const ast = parse(template.trim(), options)
      if (options.optimize !== false) {
        optimize(ast, options)
      }
      const code = generate(ast, options)
      return {
        ast,
        render: code.render,
        staticRenderFns: code.staticRenderFns
      }
    })

然后我们可以看到generate方法,vue/src/compiler/codegen/index.js:

export function generate (
      ast: ASTElement | void,
      options: CompilerOptions
    ): CodegenResult {
      const state = new CodegenState(options)
      const code = ast ? genElement(ast, state) : '_c("div")'
      return {
        render: `with(this){return ${code}}`,
        staticRenderFns: state.staticRenderFns
      }
    }

可以看到,返回的结果中render为with(this)\{return \_c(“div”)\}或者是由genElement方法返回的code字符串:

export function genElement (el: ASTElement, state: CodegenState): string {
      if (el.staticRoot && !el.staticProcessed) {
        return genStatic(el, state)
      } else if (el.once && !el.onceProcessed) {
        return genOnce(el, state)
      } else if (el.for && !el.forProcessed) {
        return genFor(el, state)
      } else if (el.if && !el.ifProcessed) {
        return genIf(el, state)
      } else if (el.tag === 'template' && !el.slotTarget) {
        return genChildren(el, state) || 'void 0'
      } else if (el.tag === 'slot') {
        return genSlot(el, state)
      } else {
        // component or element
        let code
        if (el.component) {
          code = genComponent(el.component, el, state)
        } else {
          const data = el.plain ? undefined : genData(el, state)
    
          const children = el.inlineTemplate ? null : genChildren(el, state, true)
          code = `_c('${el.tag}'${
            data ? `,${data}` : '' // data
          }${
            children ? `,${children}` : '' // children
          })`
        }
        // module transforms
        for (let i = 0; i < state.transforms.length; i++) {
          code = state.transforms[i](el, code)
        }
        return code
      }
    }

我们可以看到有genStatic、genOnce、genFor等等…

// hoist static sub-trees out
    function genStatic (el: ASTElement, state: CodegenState): string {
      el.staticProcessed = true
      state.staticRenderFns.push(`with(this){return ${genElement(el, state)}}`)
      return `_m(${
        state.staticRenderFns.length - 1
      }${
        el.staticInFor ? ',true' : ''
      })`
    }

所以最后返回的就是“\_m()、\_o()”这样的~~

好啦,看完这个我们可能会疑惑,为什么render方法是字符串呢? 不应该是返回的方法吗? 我们继续往后看哈~

vue/src/compiler/index.js:

/* @flow */
    
    import { parse } from './parser/index'
    import { optimize } from './optimizer'
    import { generate } from './codegen/index'
    import { createCompilerCreator } from './create-compiler'
    
    // `createCompilerCreator` allows creating compilers that use alternative
    // parser/optimizer/codegen, e.g the SSR optimizing compiler.
    // Here we just export a default compiler using the default parts.
    export const createCompiler = createCompilerCreator(function baseCompile (
      template: string,
      options: CompilerOptions
    ): CompiledResult {
      const ast = parse(template.trim(), options)
      if (options.optimize !== false) {
        optimize(ast, options)
      }
      const code = generate(ast, options)
      return {
        ast,
        render: code.render,
        staticRenderFns: code.staticRenderFns
      }
    })

然后我们看createCompilerCreator方法,vue/src/compiler/create-compiler.js:

import { extend } from 'shared/util'
    import { detectErrors } from './error-detector'
    import { createCompileToFunctionFn } from './to-function'
    
    export function createCompilerCreator (baseCompile: Function): Function {
      return function createCompiler (baseOptions: CompilerOptions) {
        function compile (
          template: string,
          options?: CompilerOptions
        ): CompiledResult {
         ....
        return {
          compile,
          compileToFunctions: createCompileToFunctionFn(compile)
        }
      }
    }

createCompileToFunctionFn方法又是啥呢?vue/src/compiler/to-function.js:

export function createCompileToFunctionFn (compile: Function): Function {
      const cache = Object.create(null)
    
      return function compileToFunctions (
        template: string,
        options?: CompilerOptions,
        vm?: Component
      ): CompiledFunctionResult {
        ...
        res.render = createFunction(compiled.render, fnGenErrors)
        res.staticRenderFns = compiled.staticRenderFns.map(code => {
          return createFunction(code, fnGenErrors)
        })
          ....
      }
    }

function createFunction (code, errors) {
      try {
        return new Function(code)
      } catch (err) {
        errors.push({ err, code })
        return noop
      }
    }

好吧,终于是看到庐山真面目了,我们返回的"\_c()、\_o()"字符串最后通过new Function(code)变成了Function对象,那么\_c()、\_o()方法又是啥呢?

vue/src/core/instance/render.js:

export function initRender (vm: Component) {
    ...
      vm._c = (a, b, c, d) => createElement(vm, a, b, c, d, false)
      ...
      export function renderMixin (Vue: Class<Component>) {
      // install runtime convenience helpers
      installRenderHelpers(Vue.prototype)
      .....
      }

vue/src/core/instance/render-helpers/index.js:

/* @flow */
    
    import { toNumber, toString, looseEqual, looseIndexOf } from 'shared/util'
    import { createTextVNode, createEmptyVNode } from 'core/vdom/vnode'
    import { renderList } from './render-list'
    import { renderSlot } from './render-slot'
    import { resolveFilter } from './resolve-filter'
    import { checkKeyCodes } from './check-keycodes'
    import { bindObjectProps } from './bind-object-props'
    import { renderStatic, markOnce } from './render-static'
    import { bindObjectListeners } from './bind-object-listeners'
    import { resolveScopedSlots } from './resolve-slots'
    
    export function installRenderHelpers (target: any) {
      target._o = markOnce
      target._n = toNumber
      target._s = toString
      target._l = renderList
      target._t = renderSlot
      target._q = looseEqual
      target._i = looseIndexOf
      target._m = renderStatic
      target._f = resolveFilter
      target._k = checkKeyCodes
      target._b = bindObjectProps
      target._v = createTextVNode
      target._e = createEmptyVNode
      target._u = resolveScopedSlots
      target._g = bindObjectListeners
    }

可以看到,不只有\_c、\_o,还有方法~,再往下就是根据标签跟属性创建对应的vnode对象了,所以整个render对象看完我们可以知道,render对象最后就是返回了一个vnode对象.

我们回到我们的mount方法,vue/src/core/instance/lifecycle.js:

可以看到,最重要的就是创建了一个Watcher对象:

new Watcher(vm, updateComponent, noop, null, true /* isRenderWatcher */)

然后传入了updateComponent方法:

updateComponent = () => {
          vm._update(vm._render(), hydrating)
        }

Watcher先介绍一下,Watcher对象可以监听响应式数据的变化,然后Watcher对象中会判断需不需要刷新组件,触发updateComponent方法,然后触发vm的\_update方法,最后更新dom~~

所以我们看一下\_update干了什么?  
vue/src/core/instance/lifecycle.js

Vue.prototype._update = function (vnode: VNode, hydrating?: boolean) {
        const vm: Component = this
        if (vm._isMounted) {
          callHook(vm, 'beforeUpdate')
        }
        const prevEl = vm.$el
        const prevVnode = vm._vnode
        const prevActiveInstance = activeInstance
        activeInstance = vm
        vm._vnode = vnode
        // Vue.prototype.__patch__ is injected in entry points
        // based on the rendering backend used.
        if (!prevVnode) {
          // initial render
          vm.$el = vm.__patch__(
            vm.$el, vnode, hydrating, false /* removeOnly */,
            vm.$options._parentElm,
            vm.$options._refElm
          )
          // no need for the ref nodes after initial patch
          // this prevents keeping a detached DOM tree in memory (#5851)
          vm.$options._parentElm = vm.$options._refElm = null
        } else {
          // updates
          vm.$el = vm.__patch__(prevVnode, vnode)
        }
        activeInstance = prevActiveInstance
        // update __vue__ reference
        if (prevEl) {
          prevEl.__vue__ = null
        }
        if (vm.$el) {
          vm.$el.__vue__ = vm
        }
        // if parent is an HOC, update its $el as well
        if (vm.$vnode && vm.$parent && vm.$vnode === vm.$parent._vnode) {
          vm.$parent.$el = vm.$el
        }
        // updated hook is called by the scheduler to ensure that children are
        // updated in a parent's updated hook.
      }

可以看到,update方法中接受到了vnode对象后,最后通过下面代码转成了dom对象:

vm.$el = vm.__patch__(prevVnode, vnode)

那么\_\_patch\_\_方法又是啥呢?vue/src/platforms/web/runtime/index.js:

Vue.prototype.__patch__ = inBrowser ? patch : noop

import * as nodeOps from 'web/runtime/node-ops'
    
    export const patch: Function = createPatchFunction({ nodeOps, modules })

我们看一下nodeOps是啥?vue/src/platforms/web/runtime/node-ops.js:

/* @flow */
    
    import { namespaceMap } from 'web/util/index'
    
    export function createElement (tagName: string, vnode: VNode): Element {
      const elm = document.createElement(tagName)
      if (tagName !== 'select') {
        return elm
      }
      // false or null will remove the attribute but undefined will not
      if (vnode.data && vnode.data.attrs && vnode.data.attrs.multiple !== undefined) {
        elm.setAttribute('multiple', 'multiple')
      }
      return elm
    }
    
    export function createElementNS (namespace: string, tagName: string): Element {
      return document.createElementNS(namespaceMap[namespace], tagName)
    }
    
    export function createTextNode (text: string): Text {
      return document.createTextNode(text)
    }
    
    export function createComment (text: string): Comment {
      return document.createComment(text)
    }
    
    export function insertBefore (parentNode: Node, newNode: Node, referenceNode: Node) {
      parentNode.insertBefore(newNode, referenceNode)
    }
    
    export function removeChild (node: Node, child: Node) {
      node.removeChild(child)
    }
    
    export function appendChild (node: Node, child: Node) {
      node.appendChild(child)
    }
    
    export function parentNode (node: Node): ?Node {
      return node.parentNode
    }
    
    export function nextSibling (node: Node): ?Node {
      return node.nextSibling
    }
    
    export function tagName (node: Element): string {
      return node.tagName
    }
    
    export function setTextContent (node: Node, text: string) {
      node.textContent = text
    }
    
    export function setStyleScope (node: Element, scopeId: string) {
      node.setAttribute(scopeId, '')
    }

翻过了一座又一座山,历经了千辛万苦,我们终于是看到了庐山真面目,小伙伴可别说你不熟悉这些代码哈~~

好啦~ 我们简单的回顾一下前面的内容哈,首先我们定义了一些响应式数据并监听变化—>执行mount方法–>生成render方法—>创建vnode对象–>通过update方法把vnode对象转换成dom元素…

好啦!! 整个vue的源码研究先到这了,之后会正对vue-loader以及watcher对象做一次解析.

[Vue源码解析之（computed&watch&观察者模式）][Vue_computed_watch]

先到这里啦，欢迎志同道合的小伙伴入群，一起交流一起学习～～ 加油骚年！！  
qq群链接:

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[Vue]: https://blog.csdn.net/vv_bug/article/details/84954607
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3Z2X2J1Zw_size_16_color_FFFFFF_t_70]: /images/20220404/8a02efe41b4a4629b96b47d022837051.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3Z2X2J1Zw_size_16_color_FFFFFF_t_70 1]: /images/20220404/b4440aa772c94e9abf5797502d2ae2e5.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3Z2X2J1Zw_size_16_color_FFFFFF_t_70 2]: /images/20220404/a1745af6a6fb475f824bd26ca0581084.png
[https_cn.vuejs.org_v2_guide_render-function.html]: https://cn.vuejs.org/v2/guide/render-function.html
[Vue_computed_watch]: https://vvbug.blog.csdn.net/article/details/102519987
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3Z2X2J1Zw_size_16_color_FFFFFF_t_70 3]: /images/20220404/3e90d1a3f54f4a2da12003ab3fb1781b.png