review

The last course talked about the initialization process of the Vue object. The first is to call the core _init() method, in which option is mounted to the VM object, and the life cycle, data, etc., is initialized. Finally, $mount method is used to mount the DOM object bound by EL. This section will look at the implementation of the $mount function.

  1. Get the EL object, convert the template to the Render function, and mount it by calling the top-level mount method

src/platform/web/entry-runtime-with-compiler.js

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
  if(! options.render) {let template = options.template
    if (template) {
      if (typeof template === 'string') {
        if (template.charAt(0) = = =The '#') {
          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 The ${this._name} compile`.'compile'.'compile end')}}}return mount.call(this, el, hydrating)
}
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  1. Call the mountComponent function

src/platform/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)
}
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  1. Instantiate Watcher and execute the callback functionupdateComponent()perform_render()with_update()

src/core/instance/lifecycle.js

export function mountComponent (vm: Component, el: ? Element, hydrating? : boolean) :Component {
  vm.$el = el
  if(! vm.$options.render) { vm.$options.render = createEmptyVNodeif(process.env.NODE_ENV ! = ='production') {
      /* istanbul ignore if */
      if ((vm.$options.template && vm.$options.template.charAt(0)! = =The '#') ||
        vm.$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, {
    before () {
      if (vm._isMounted) {
        callHook(vm, 'beforeUpdate')}}},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
}
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Tips: The _render() function generates the virtual DOM and then passes it to _update() to update the final DOM. The updateComponent() function is actually executed for data updates and so on