Vue2 原始碼漫遊（二）
描述：
在（一）中其實已經把Vue作為MVVM的框架中資料流相關跑了一遍。這一章我們先看mount這一步，這樣Vue大的主線就基本跑通了。然後我們再去看compile，v-bind等功能性模組的處理。一、出發點
path:
platformswebentry-runtime-with-compiler.js
這裡對原本的公用$mount方法進行了代理.實際的直接方法是core/instance/lifecycle.js中的mountComponent方法。
根據元件模板的不同形式這裡出現了兩個分支，一個核心：
分支：
1、元件引數中有render屬性：執行mount.call(this, el, hydrating)
2、元件引數中沒有render屬性：將template/el轉換為render方法
核心：Vue.prototype._render公共方法
/* @flow */
import config from `core/config`
import { warn, cached } from `core/util/index`
import { mark, measure } from `core/util/perf`
import Vue from `./runtime/index`
import { query } from `./util/index`
import { compileToFunctions } from `./compiler/index`
import { shouldDecodeNewlines, shouldDecodeNewlinesForHref } from `./util/compat`
const idToTemplate = cached(id => {
const el = query(id)
return el && el.innerHTML
})
//這裡代理了vue例項的$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轉化為render方法。這裡就是一個大的分支，我們可以將它稱為render分支
if (!options.render) {
//如果沒有傳入render方法，且template引數存在，那麼就開始解析模板，這就是compile的開始
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 ${this._name} compile`, `compile`, `compile end`)
}
}
}
//呼叫公用mount方法
return mount.call(this, el, hydrating)
}
/**
* Get outerHTML of elements, taking care
* of SVG elements in IE as well.
*/
function getOuterHTML (el: Element): string {
if (el.outerHTML) {
return el.outerHTML
} else {
const container = document.createElement(`div`)
container.appendChild(el.cloneNode(true))
return container.innerHTML
}
}
Vue.compile = compileToFunctions
export default Vue
1、元件中有render屬性
//最常見
new Vue({
el: `#app`,
router,
render: h => h(App),
});如果有render方法，那麼就會呼叫公共mount方法，然後判斷一下平臺後直接呼叫mountComponent方法
// public mount method
//入口中被代理的公用方法就是它，path : platformsweb
untimeindex.js
Vue.prototype.$mount = function (
el?: string | Element,
hydrating?: boolean
): Component {
//因為是公用方法所以在這裡有重新判斷了一些el，其實如果有render屬性的話，這裡el就已經是DOM物件了
el = el && inBrowser ? query(el) : undefined
return mountComponent(this, el, hydrating)
}接下來就是mountComponent。這裡面有一個關鍵點 vm._watcher = new Watcher(vm, updateComponent, noop)，這個其實就是上篇中說到的依賴收集的一個觸發點。你可以想想，元件在這個時候其實資料已經完成了響應式轉換，就坐等收集依賴了，也就是坐等被第一次使用訪問了。
export function mountComponent (
vm: Component,
el: ?Element,
hydrating?: boolean
): Component {
vm.$el = el
//這個判斷其實只是在配置預設render方法createEmptyVNode
if (!vm.$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
)
}
}
}
//執行beforeMount回撥函式
callHook(vm, `beforeMount`)
//這個updateComponent方法很重要，其實可以將它與Watcher中的引數expOrFn聯絡起來。他就是一個Watcher例項的值的獲取過程，訂閱者的一種真實身份。
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 ${name} patch`, startTag, endTag)
}
} else {
updateComponent = () => {
//實際方法,被Watcher.getter方法的執行給呼叫回來了，在這裡先直接執行vm.render，這個就是compile的觸發點
vm._update(vm._render(), hydrating)
}
}
//開始生產updateComponent這個動作的訂閱者了，生產過程中呼叫Watcher.getter方法時又會回來執行這個updateComponent方法。看上面兩排
vm._watcher = new Watcher(vm, updateComponent, noop)
hydrating = false
// manually mounted instance, call mounted on self
// mounted is called for render-created child components in its inserted hook
if (vm.$vnode == null) {
vm._isMounted = true
callHook(vm, `mounted`)
}
return vm
}2、公共render方法
path : coreinstance
ender.js
Vue.prototype._render()這個方法的呼叫在整個原始碼中就兩處，vm._render()和child._render()。
從中可以理解到一個執行鏈條：
$mount -> new Watcher -> watcher.getter -> updateComponent -> vm._update -> vm._render -> vm.createElement -> createComponent(如果存在子元件，呼叫createElement，如果沒有執行createElement)
在render的這一個層面上的出發點，都是來自於vm.$options.render函式，這也是為什麼在Vue.prototype.$mount方法中會對vm.$options.render進行判斷處理從而分出有render函式和沒有render函式兩種不同的處理方式
看一下vm._render原始碼：
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
//如果父元件還沒有更新，那麼就先把子元件存在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 {
//執行$options.render,如果沒傳的就是一個預設的VNode例項。最後都會去掉用createElement公用方法corevdomcreate-element.js。這個就是大工程了。
vnode = render.call(vm._renderProxy, vm.$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 : corevdomcreate-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: ${JSON.stringify(data)}
` +
`Always create fresh vnode data objects in each render!`,
context
)
return createEmptyVNode()
}
// object syntax in v-bind
if (isDef(data) && isDef(data.is)) {
tag = data.is
}
if (!tag) {
// in case of component :is set to falsy value
return createEmptyVNode()
}
// warn against non-primitive key
if (process.env.NODE_ENV !== `production` &&
isDef(data) && isDef(data.key) && !isPrimitive(data.key)
) {
warn(
`Avoid using non-primitive value as key, ` +
`use string/number value instead.`,
context
)
}
// support single function children as default scoped slot
if (Array.isArray(children) &&
typeof children[0] === `function`
) {
data = data || {}
data.scopedSlots = { default: children[0] }
children.length = 0
}
if (normalizationType === ALWAYS_NORMALIZE) {
children = normalizeChildren(children)
} else if (normalizationType === SIMPLE_NORMALIZE) {
children = simpleNormalizeChildren(children)
}
let vnode, ns
if (typeof tag === `string`) {
let Ctor
ns = (context.$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 : corevdomcreate-component.js
createComponent (Ctor, data, context, children, tag)
Ctor : 元件Module資訊，最後與會被處理成vm例項物件
data ： 元件資料
context : 當前Vue元件
children : 自元件
tag ：元件名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不能為undefined || null
if (isUndef(Ctor)) {
return
}
//
const baseCtor = context.$options._base
// plain options object: turn it into a constructor
// 如果Ctor為物件，合併到vm資料，構建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: ${String(Ctor)}`, context)
}
return
}
// 非同步元件
let asyncFactory
if (isUndef(Ctor.cid)) {
asyncFactory = Ctor
Ctor = resolveAsyncComponent(asyncFactory, baseCtor, context)
if (Ctor === undefined) {
// return a placeholder node for async component, which is rendered
// as a comment node but preserves all the raw information for the node.
// the information will be used for async server-rendering and hydration.
return createAsyncPlaceholder(
asyncFactory,
data,
context,
children,
tag
)
}
}
data = data || {}
// resolve constructor options in case global mixins are applied after
// component constructor creation
//解析元件例項的options
resolveConstructorOptions(Ctor)
// transform component v-model data into props & events
if (isDef(data.model)) {
transformModel(Ctor.options, data)
}
// extract props
const propsData = extractPropsFromVNodeData(data, Ctor, tag)
// functional component
if (isTrue(Ctor.options.functional)) {
return createFunctionalComponent(Ctor, propsData, data, context, children)
}
// extract listeners, since these needs to be treated as
// child component listeners instead of DOM listeners
const listeners = data.on
// replace with listeners with .native modifier
// so it gets processed during parent component patch.
data.on = data.nativeOn
if (isTrue(Ctor.options.abstract)) {
// abstract components do not keep anything
// other than props & listeners & slot
// work around flow
const slot = data.slot
data = {}
if (slot) {
data.slot = slot
}
}
// merge component management hooks onto the placeholder node
// 合併鉤子函式 init 、 destroy 、 insert 、prepatch
mergeHooks(data)
// return a placeholder vnode
// 最終目的生成一個vnode，然後就是一路的return出去
const name = Ctor.options.name || tag
const vnode = new VNode(
`vue-component-${Ctor.cid}${name ? `-${name}` : ``}`,
data, undefined, undefined, undefined, context,
{ Ctor, propsData, listeners, tag, children },
asyncFactory
)
return vnode
}總結：
過程線條：
$mount -> new Watcher -> watcher.getter -> updateComponent -> vm._update -> vm._render -> vm.createElement -> createComponent(如果存在子元件，呼叫createElement，如果沒有執行createElement)上面這個線條中其實都圍繞著vm.$options進行render元件。現在大部分專案都是使用的.vue元件進行開發，所以使得對元件的配置物件不太敏感。
因為將.vue的內容轉化為Vue元件配置模式的過程都被vue-loader處理（我們在require元件時處理的），其中就包括將template轉換為render函式的關鍵。我們也可以定義一個配置型的元件，然後觸發Vue$3.prototype.$mount中的mark(`compile`)進行處理。但是我覺得意義不是太大。
過程，這也是導致我們在原始碼執行中總是看見在有無render函式分支，的時候總是能看見render函式，然後就進入對元件 vm._update(vm._render(), hydrating)。
我們先記住這條主線，下一章我們進入到vue-loader中去看看