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
