vue源码解读系列（5）：分析dom挂载阶段，了解$mount的实现
入口文件：
这里先缓存了起来，const mount = Vue.prototype.$mount，这里的 Vue.prototype.$mount 是在 ./runtime/index 中定义的。这里是复用了 runtime only 版本初始化生命周期的一些代码，因为runtime only 版本是没有挂载 dom 的，所以要在这里重新写挂载dom的代码，如下：
// src/platforms/web/entry-runtime-with-compiler.js
import Vue from './runtime/index'
const mount = Vue.prototype.$mount
Vue.prototype.$mount = function (
el?: string | Element,
hydrating?: boolean
): Component {
// query(el) 会判断是字符串就报警告并返回一个空的div，是dom就直接返回一个dom，所以我们一般就是
el = el && query(el)
/* istanbul ignore if */
// 这里判断你传入的 dom 不能是body或者 html，因为你会把整个body覆盖
if (el === document.body || el === document.documentElement) {
process.env.NODE_ENV !== 'production' && warn(
`Do not mount Vue to or - mount to normal elements instead.`
)
return this
}
const options = this.$options
// resolve template/el and convert to render function
// 这里判断不是render函数（写template模板）的处理
if (!options.render) {
// 拿到template
let template = options.template
if (template) {
// 如果template是字符串
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
)
}
}
// 如果template是标签
} else if (template.nodeType) {
template = template.innerHTML
} else {
// 如果template是其他，报警告
if (process.env.NODE_ENV !== 'production') {
warn('invalid template option:' + template, this)
}
return this
}
} else if (el) {
// 拿到这个字符串
template = getOuterHTML(el)
}
// 以下就是编译相关了
if (template) {
/* istanbul ignore if */
if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
mark('compile')
}
const {
render, staticRenderFns } = compileToFunctions(template, {
outputSourceRange: process.env.NODE_ENV !== 'production',
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 ${
this._name} compile`, 'compile', 'compile end')
}
}
}
// 如果有render函数，就执行这个
// mount就是之前缓存的Vue.prototype.$mount，也就是runtime/index.js里面定义的，里面返回了mountComponent函数，我们来看看mountComponent里面是什么，下一个
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
// src/core/instance/lifecycle.js
export function mountComponent (
vm: Component,
el: ?Element,
hydrating?: boolean
): Component {
vm.$el = el
if (!vm.$options.render) {
vm.$options.render = createEmptyVNode
if (process.env.NODE_ENV !== 'production') {
/* istanbul ignore if */
if ((vm.$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
)
}
}
}
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 = () => {
// 下一个
vm._update(vm._render(), hydrating)
}
}
// we set this to vm._watcher inside the watcher's constructor
// since the watcher's initial patch may call $forceUpdate (e.g. inside child
// component's mounted hook), which relies on vm._watcher being already defined
new Watcher(vm, updateComponent, noop, {
before () {
if (vm._isMounted && !vm._isDestroyed) {
callHook(vm, 'beforeUpdate')
}
}
}, true /* isRenderWatcher */)
hydrating = false
// manually mounted instance, call mounted on self
// mounted is called for render-created child components in its inserted hook
if (vm.$vnode == null) {
vm._isMounted = true
callHook(vm, 'mounted')
}
return vm
}
import Vue form 'vue'
var app = new Vue({
// render和 el写一个就好
render: h => h(App),
el: '#app',
data () {
message: 'hello word'
},
render (h) {
return h('div', {
class: 'menu-nav'
})
}
})