Vue2 源码漫游(二)

Vue2 源码漫游(二)

描述:

    在(一)中其实已经把Vue作为MVVM的框架中数据流相关跑了一遍。这一章我们先看mount这一步,这样Vue大的主线就基本跑通了。然后我们再去看compile,v-bind等功能性模块的处理。

一、出发点

path:
    platforms\web\entry-runtime-with-compiler.js
这里对原本的公用$mount方法进行了代理.实际的直接方法是core/instance/lifecycle.js中的mountComponent方法。
根据组件模板的不同形式这里出现了两个分支,一个核心:
    分支:
        1、组件参数中有render属性:执行mount.call(this, el, hydrating)
        2、组件参数中没有render属性:将template/el转换为render方法
    核心:Vue.prototype._render公共方法
/* @flow */

import config from 'core/config'
import { warn, cached } from 'core/util/index'
import { mark, measure } from 'core/util/perf'

import Vue from './runtime/index'
import { query } from './util/index'
import { compileToFunctions } from './compiler/index'
import { shouldDecodeNewlines, shouldDecodeNewlinesForHref } from './util/compat'

const idToTemplate = cached(id => {
  const el = query(id)
  return el && el.innerHTML
})
//这里代理了vue实例的$mount方法
const mount = Vue.prototype.$mount
Vue.prototype.$mount = function (
  el?: string | Element,
  hydrating?: boolean
): Component {
  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
  // resolve template/el and convert to render function
  //解析template/el转化为render方法。这里就是一个大的分支,我们可以将它称为render分支
  if (!options.render) {
    //如果没有传入render方法,且template参数存在,那么就开始解析模板,这就是compile的开始
    let template = options.template
    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) {
      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')
      }
    }
  }
  //调用公用mount方法
  return mount.call(this, el, hydrating)
}

/**
 * Get outerHTML of elements, taking care
 * of SVG elements in IE as well.
 */
function getOuterHTML (el: Element): string {
  if (el.outerHTML) {
    return el.outerHTML
  } else {
    const container = document.createElement('div')
    container.appendChild(el.cloneNode(true))
    return container.innerHTML
  }
}

Vue.compile = compileToFunctions

export default Vue

1、组件中有render属性

//最常见
new Vue({
    el: '#app',
    router,
    render: h => h(App),
});

如果有render方法,那么就会调用公共mount方法,然后判断一下平台后直接调用mountComponent方法

// public mount method
//入口中被代理的公用方法就是它,path : platforms\web\runtime\index.js
Vue.prototype.$mount = function (
  el?: string | Element,
  hydrating?: boolean
): Component {
  //因为是公用方法所以在这里有重新判断了一些el,其实如果有render属性的话,这里el就已经是DOM对象了
  el = el && inBrowser ? query(el) : undefined
  return mountComponent(this, el, hydrating)
}

接下来就是mountComponent。这里面有一个关键点 vm._watcher = new Watcher(vm, updateComponent, noop),这个其实就是上篇中说到的依赖收集的一个触发点。你可以想想,组件在这个时候其实数据已经完成了响应式转换,就坐等收集依赖了,也就是坐等被第一次使用访问了。

export function mountComponent (
  vm: Component,
  el: ?Element,
  hydrating?: boolean
): Component {
  vm.$el = el
  //这个判断其实只是在配置默认render方法createEmptyVNode
  if (!vm.$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
        )
      }
    }
  }
  //执行beforeMount回调函数
  callHook(vm, 'beforeMount')

  //这个updateComponent方法很重要,其实可以将它与Watcher中的参数expOrFn联系起来。他就是一个Watcher实例的值的获取过程,订阅者的一种真实身份。
  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 = () => {
      //实际方法,被Watcher.getter方法的执行给调用回来了,在这里先直接执行vm.render,这个就是compile的触发点
      vm._update(vm._render(), hydrating)
    }
  }
  //开始生产updateComponent这个动作的订阅者了,生产过程中调用Watcher.getter方法时又会回来执行这个updateComponent方法。看上面两排
  vm._watcher = new Watcher(vm, updateComponent, noop)
  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
}

2、公共render方法

path : core\instance\render.js
Vue.prototype._render()这个方法的调用在整个源码中就两处,vm._render()和child._render()。
从中可以理解到一个执行链条:

$mount -> new Watcher -> watcher.getter -> updateComponent -> vm._update -> vm._render -> vm.createElement -> createComponent(如果存在子组件,调用createElement,如果没有执行createElement)
在render的这一个层面上的出发点,都是来自于vm.$options.render函数,这也是为什么在Vue.prototype.$mount方法中会对vm.$options.render进行判断处理从而分出有render函数和没有render函数两种不同的处理方式

看一下vm._render源码:


export function renderMixin (Vue: Class<Component>) {
  // install runtime convenience helpers
  installRenderHelpers(Vue.prototype)

  Vue.prototype.$nextTick = function (fn: Function) {
    return nextTick(fn, this)
  }

  Vue.prototype._render = function (): VNode {
    const vm: Component = this
    const { render, _parentVnode } = vm.$options
    
    //如果父组件还没有更新,那么就先把子组件存在vm.$slots中
    if (vm._isMounted) {
      // if the parent didn't update, the slot nodes will be the ones from
      // last render. They need to be cloned to ensure "freshness" for this render.
      for (const key in vm.$slots) {
        const slot = vm.$slots[key]
        if (slot._rendered) {
          vm.$slots[key] = cloneVNodes(slot, true /* deep */)
        }
      }
    }
    //作用域插槽
    vm.$scopedSlots = (_parentVnode && _parentVnode.data.scopedSlots) || emptyObject

    // set parent vnode. this allows render functions to have access
    // to the data on the placeholder node.
    vm.$vnode = _parentVnode
    // render self
    let vnode
    try {
      //执行$options.render,如果没传的就是一个默认的VNode实例。最后都会去掉用createElement公用方法core\vdom\create-element.js。这个就是大工程了。
      vnode = render.call(vm._renderProxy, vm.$createElement)
    } catch (e) {
      handleError(e, vm, `render`)
      // return error render result,
      // or previous vnode to prevent render error causing blank component
      /* istanbul ignore else */
      if (process.env.NODE_ENV !== 'production') {
        if (vm.$options.renderError) {
          try {
            vnode = vm.$options.renderError.call(vm._renderProxy, vm.$createElement, e)
          } catch (e) {
            handleError(e, vm, `renderError`)
            vnode = vm._vnode
          }
        } else {
          vnode = vm._vnode
        }
      } else {
        vnode = vm._vnode
      }
    }
    // return empty vnode in case the render function errored out
    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
  }
}

3、_createElement, createComponent


path : core\vdom\create-element.js
_createElement(context, tag, data, children, normalizationType)
export function _createElement (
  context: Component,
  tag?: string | Class<Component> | Function | Object,
  data?: VNodeData,
  children?: any,
  normalizationType?: number
): VNode {
  //可以使用
  if (isDef(data) && isDef((data: any).__ob__)) {
    process.env.NODE_ENV !== 'production' && warn(
      `Avoid using observed data object as vnode data: ${JSON.stringify(data)}\n` +
      'Always create fresh vnode data objects in each render!',
      context
    )
    return createEmptyVNode()
  }
  // object syntax in v-bind
  if (isDef(data) && isDef(data.is)) {
    tag = data.is
  }
  if (!tag) {
    // in case of component :is set to falsy value
    return createEmptyVNode()
  }
  // warn against non-primitive key
  if (process.env.NODE_ENV !== 'production' &&
    isDef(data) && isDef(data.key) && !isPrimitive(data.key)
  ) {
    warn(
      'Avoid using non-primitive value as key, ' +
      'use string/number value instead.',
      context
    )
  }
  // support single function children as default scoped slot
  if (Array.isArray(children) &&
    typeof children[0] === 'function'
  ) {
    data = data || {}
    data.scopedSlots = { default: children[0] }
    children.length = 0
  }
  if (normalizationType === ALWAYS_NORMALIZE) {
    children = normalizeChildren(children)
  } else if (normalizationType === SIMPLE_NORMALIZE) {
    children = simpleNormalizeChildren(children)
  }
  let vnode, ns
  if (typeof tag === 'string') {
    let Ctor
    ns = (context.$vnode && context.$vnode.ns) || config.getTagNamespace(tag)
    if (config.isReservedTag(tag)) {
      // platform built-in elements
      vnode = new VNode(
        config.parsePlatformTagName(tag), data, children,
        undefined, undefined, context
      )
    } else if (isDef(Ctor = resolveAsset(context.$options, 'components', tag))) {
      // component
      vnode = createComponent(Ctor, data, context, children, tag)
    } else {
      // unknown or unlisted namespaced elements
      // check at runtime because it may get assigned a namespace when its
      // parent normalizes children
      vnode = new VNode(
        tag, data, children,
        undefined, undefined, context
      )
    }
  } else {
    // direct component options / constructor
    vnode = createComponent(tag, data, context, children)
  }
  if (isDef(vnode)) {
    if (ns) applyNS(vnode, ns)
    return vnode
  } else {
    return createEmptyVNode()
  }
}
    path : core\vdom\create-component.js
    createComponent (Ctor, data, context, children, tag)
        Ctor : 组件Module信息,最后与会被处理成vm实例对象
        data : 组件数据
        context : 当前Vue组件
        children : 自组件
        tag :组件名
const hooksToMerge = Object.keys(componentVNodeHooks)

export function createComponent (
  Ctor: Class<Component> | Function | Object | void,
  data: ?VNodeData,
  context: Component,
  children: ?Array<VNode>,
  tag?: string
): VNode | void {

  //Ctor不能为undefined || null
  if (isUndef(Ctor)) {
    return
  }
  //
  const baseCtor = context.$options._base

  // plain options object: turn it into a constructor
  // 如果Ctor为对象,合并到vm数据,构建Ctor
  if (isObject(Ctor)) {
    Ctor = baseCtor.extend(Ctor)
  }

  // if at this stage it's not a constructor or an async component factory,
  // reject.
  if (typeof Ctor !== 'function') {
    if (process.env.NODE_ENV !== 'production') {
      warn(`Invalid Component definition: ${String(Ctor)}`, context)
    }
    return
  }

  // 异步组件
  let asyncFactory
  if (isUndef(Ctor.cid)) {
    asyncFactory = Ctor
    Ctor = resolveAsyncComponent(asyncFactory, baseCtor, context)
    if (Ctor === undefined) {
      // return a placeholder node for async component, which is rendered
      // as a comment node but preserves all the raw information for the node.
      // the information will be used for async server-rendering and hydration.
      return createAsyncPlaceholder(
        asyncFactory,
        data,
        context,
        children,
        tag
      )
    }
  }

  data = data || {}

  // resolve constructor options in case global mixins are applied after
  // component constructor creation
  //解析组件实例的options
  resolveConstructorOptions(Ctor)

  // transform component v-model data into props & events
  if (isDef(data.model)) {
    transformModel(Ctor.options, data)
  }

  // extract props
  const propsData = extractPropsFromVNodeData(data, Ctor, tag)

  // functional component
  if (isTrue(Ctor.options.functional)) {
    return createFunctionalComponent(Ctor, propsData, data, context, children)
  }

  // extract listeners, since these needs to be treated as
  // child component listeners instead of DOM listeners
  const listeners = data.on
  // replace with listeners with .native modifier
  // so it gets processed during parent component patch.
  data.on = data.nativeOn

  if (isTrue(Ctor.options.abstract)) {
    // abstract components do not keep anything
    // other than props & listeners & slot

    // work around flow
    const slot = data.slot
    data = {}
    if (slot) {
      data.slot = slot
    }
  }

  // merge component management hooks onto the placeholder node
  // 合并钩子函数 init 、 destroy  、 insert 、prepatch
  mergeHooks(data)

  // return a placeholder vnode
 // 最终目的生成一个vnode,然后就是一路的return出去
  const name = Ctor.options.name || tag
  const vnode = new VNode(
    `vue-component-${Ctor.cid}${name ? `-${name}` : ''}`,
    data, undefined, undefined, undefined, context,
    { Ctor, propsData, listeners, tag, children },
    asyncFactory
  )
  return vnode
}

总结:

过程线条:

$mount -> new Watcher -> watcher.getter -> updateComponent -> vm._update -> vm._render -> vm.createElement -> createComponent(如果存在子组件,调用createElement,如果没有执行createElement)

上面这个线条中其实都围绕着vm.$options进行render组件。现在大部分项目都是使用的.vue组件进行开发,所以使得对组件的配置对象不太敏感。
因为将.vue的内容转化为Vue组件配置模式的过程都被vue-loader处理(我们在require组件时处理的),其中就包括将template转换为render函数的关键。我们也可以定义一个配置型的组件,然后触发Vue$3.prototype.$mount中的mark(‘compile’)进行处理。但是我觉得意义不是太大。
过程,这也是导致我们在源码运行中总是看见在有无render函数分支,的时候总是能看见render函数,然后就进入对组件 vm._update(vm._render(), hydrating)。
我们先记住这条主线,下一章我们进入到vue-loader中去看看

    原文作者:daipeng7
    原文地址: https://segmentfault.com/a/1190000012002376
    本文转自网络文章,转载此文章仅为分享知识,如有侵权,请联系博主进行删除。
点赞