Vue技术内幕 出去看看吧 挂载

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

updateComponent = () => {
      vm._update(vm._render(), hydrating)
    }
//...
  new Watcher(vm, updateComponent, noop, {
    before () {
      if (vm._isMounted) {
        callHook(vm, ‘beforeUpdate‘)
      }
    }
  }, true /* isRenderWatcher */)

src\core\instance\render.js

Vue.prototype._render = function (): VNode {
    const vm: Component = this
    const { render, _parentVnode } = vm.$options
　　 //...
    // set parent vnode. this allows render functions to have access
    // to the data on the placeholder node.
    vm.$vnode = _parentVnode
    // render self
    let vnode
    try {
      vnode = render.call(vm._renderProxy, vm.$createElement)