关于vue.js:vue源码分析二从new-Vue到渲染到页面

_init 办法

new Vue()会执行 Vue 构造函数的_init 办法，_init 办法被 initMixin 中扩大的，src\core\instance\init.js

export function initMixin (Vue: Class<Component>) {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
    // 合并配置
    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
    // vue 实例 vm 扩大
    // 生命周期
    initLifecycle(vm)
    // 事件
    initEvents(vm)
    // 渲染
    // createElement 也就是咱们手写 render 函数的参数 h
    // slots
    initRender(vm)
    // 第一个生命周期
    // data,props 还没有
    callHook(vm, 'beforeCreate')
    // inject 的实现，在 provide 之前
    initInjections(vm) // resolve injections before data/props
    // props，data,computed,methods 都在这里，须要重点看，所以 beforCreate 钩子函数中无奈读取 props 和 data 的变量
    initState(vm)
    // provide 的实现
    initProvide(vm) // resolve provide after data/props
    // 第二个生命周期，这是能够获取到 data,props,computed,methods
    // 所有的生命周期函数都是调用的 callHook 函数
    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)
    }
    // 如果有 el，则调用 $mount
    if (vm.$options.el) {vm.$mount(vm.$options.el)
    }
  }
}

_init 办法次要做的就是合并配置，初始化生命周期，初始化事件核心，初始化渲染，初始化 data、props、computed、watcher 等等

挂载 $mount

如果实例化的时候提供了 el 属性，就执行 vm.$mount(vm.$options.el)，如果没有提供就执行 new Vue().$mount(‘#app’),$mount 办法定义在 src\platforms\web\runtime\index.js

// 这是 web 环境，如果是服务端渲染为 noop(空函数)，否则为 patch
Vue.prototype.__patch__ = inBrowser ? patch : noop

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

最终调用的是 mountComponent，定义在 src\core\instance\lifecycle.js

// 此办法外围就是先实例化一个渲染 Watcher，在它的回调函数中会调用 updateComponent 办法，// 在此办法中调用 vm._render 办法学生成虚构 Node，最终调用 vm._update 更新 DOM
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
        )
      }
    }
  }
  // 调用 beforeMount 生命周期函数
  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)
      // vm._render 最终是通过执行 createElement 办法并返回的是 vnode
      // 调用 vm._render()生成虚构 dom，vm._render()调用 vm.$options.render 函数
      const vnode = vm._render()
      mark(endTag)
      measure(`vue ${name} render`, startTag, endTag)

      mark(startTag)
      // 调用 vm._update 更新 dom
      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
  // Watcher 做什么用？// Watcher 在这里起到两个作用，一个是初始化的时候会执行回调函数 updateComponent
  // 另一个是当 vm 实例中的监测的数据发生变化的时候执行回调函数
  new Watcher(vm, updateComponent, noop, {before () {if (vm._isMounted && !vm._isDestroyed) {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
  // vm.$vnode 指的是父组件虚构 dom
  if (vm.$vnode == null) {
    vm._isMounted = true
    // 调用 mounted 生命周期函数
    callHook(vm, 'mounted')
  }
  return vm
}

mountComponent 办法有三个外围：vm._render()，vm._update()，new Watcher（）。renderMixin 函数在 Vue 的原型上挂载了_render 办法，src\core\instance\render.js

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

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

  // 虚构 dom
  Vue.prototype._render = function (): VNode {
    const vm: Component = this
    const {render, _parentVnode} = vm.$options
    ...
    let vnode
      // 渲染函数是实例公有的，有一个参数 createElement，createElement 就是 vm.$createElement, 它的定义是在执行 initRender 时
      // render 就是 vm.option.render, 承受 vm.$createElement(别名为 h)作为参数：render: h => h(App)
      // vm.$createElement 在 initRender 中定义
      vnode = render.call(vm._renderProxy, vm.$createElement)
   ..
      vnode = createEmptyVNode()}
    // set parent
    // _parentVnode 就是 vm.$vnode
    vnode.parent = _parentVnode
    return vnode
  }
}

vm_render()最终调用 vm.$options.render, 并且传递了 vm.$createElemnt, 定义在 initRender()中。render 函数的返回是 createElemnt 办法生成的 vnode，通过 new VNode()生产 vnode。
vm._update 放在执行 lifecycleMixin()是挂载到 Vue 原型上的，src\core\instance\lifecycle.js

// 此办法外围时调用了 vm.__patch__办法（src/platforms/web/runtime/index.js）Vue.prototype._update = function (vnode: VNode, hydrating?: boolean) {
    const vm: Component = this
    const prevEl = vm.$el
    const prevVnode = vm._vnode
    const restoreActiveInstance = setActiveInstance(vm)
    vm._vnode = vnode
    // Vue.prototype.__patch__ is injected in entry points
    // based on the rendering backend used.
    if (!prevVnode) {
      // initial render
      vm.$el = vm.__patch__(vm.$el, vnode, hydrating, false /* removeOnly */)
    } else {
      // updates
      vm.$el = vm.__patch__(prevVnode, vnode)
    }
    restoreActiveInstance()
    // 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.
  }

最终调用 vm.__patch__办法，定义在__patch__办法调用了 createPatchFunction，src\core\vdom\patch.js

return function patch (oldVnode, vnode, hydrating, removeOnly) {if (isUndef(vnode)) {if (isDef(oldVnode)) invokeDestroyHook(oldVnode)
      return
    }

    let isInitialPatch = false
    const insertedVnodeQueue = []

    if (isUndef(oldVnode)) {// empty mount (likely as component), create new root element
      isInitialPatch = true
      createElm(vnode, insertedVnodeQueue)
    } else {const isRealElement = isDef(oldVnode.nodeType)
      if (!isRealElement && sameVnode(oldVnode, vnode)) {
        // patch existing root node
        patchVnode(oldVnode, vnode, insertedVnodeQueue, null, null, removeOnly)
      } else {if (isRealElement) {
          // mounting to a real element
          // check if this is server-rendered content and if we can perform
          // a successful hydration.
          if (oldVnode.nodeType === 1 && oldVnode.hasAttribute(SSR_ATTR)) {oldVnode.removeAttribute(SSR_ATTR)
            hydrating = true
          }
          if (isTrue(hydrating)) {if (hydrate(oldVnode, vnode, insertedVnodeQueue)) {invokeInsertHook(vnode, insertedVnodeQueue, true)
              return oldVnode
            } else if (process.env.NODE_ENV !== 'production') {
              warn(
                'The client-side rendered virtual DOM tree is not matching' +
                'server-rendered content. This is likely caused by incorrect' +
                'HTML markup, for example nesting block-level elements inside' +
                '<p>, or missing <tbody>. Bailing hydration and performing' +
                'full client-side render.'
              )
            }
          }
          // either not server-rendered, or hydration failed.
          // create an empty node and replace it
          oldVnode = emptyNodeAt(oldVnode)
        }

        // replacing existing element
        const oldElm = oldVnode.elm
        const parentElm = nodeOps.parentNode(oldElm)

        // create new node
        createElm(
          vnode,
          insertedVnodeQueue,
          // extremely rare edge case: do not insert if old element is in a
          // leaving transition. Only happens when combining transition +
          // keep-alive + HOCs. (#4590)
          oldElm._leaveCb ? null : parentElm,
          nodeOps.nextSibling(oldElm)
        )

        // update parent placeholder node element, recursively
        if (isDef(vnode.parent)) {
          let ancestor = vnode.parent
          const patchable = isPatchable(vnode)
          while (ancestor) {for (let i = 0; i < cbs.destroy.length; ++i) {cbs.destroy[i](ancestor)
            }
            ancestor.elm = vnode.elm
            if (patchable) {for (let i = 0; i < cbs.create.length; ++i) {cbs.create[i](emptyNode, ancestor)
              }
              // #6513
              // invoke insert hooks that may have been merged by create hooks.
              // e.g. for directives that uses the "inserted" hook.
              const insert = ancestor.data.hook.insert
              if (insert.merged) {
                // start at index 1 to avoid re-invoking component mounted hook
                for (let i = 1; i < insert.fns.length; i++) {insert.fns[i]()}
              }
            } else {registerRef(ancestor)
            }
            ancestor = ancestor.parent
          }
        }

        // destroy old node
        if (isDef(parentElm)) {removeVnodes([oldVnode], 0, 0)
        } else if (isDef(oldVnode.tag)) {invokeDestroyHook(oldVnode)
        }
      }
    }

    invokeInsertHook(vnode, insertedVnodeQueue, isInitialPatch)
    return vnode.elm
  }

path 办法外围是调用 createElm 办法，createElm 调用 insert，insert 办法将 vnode 通过原生办法 appendChild 插入到 app 标签中，实际上整个过程就是递归创立了一个残缺的 DOM 树并插入到 #app 父级标签上
有这样一个列子

var app = new Vue({
  el: '#app',
  render: function (createElement) {
    return createElement('div', {
      attrs: {id: 'app'},
    }, this.message)
  },
  data: {message: 'Hello Vue!'}
})

new Vue 的残缺流程