前言
前面我们简单的了解了 vue 初始化时的一些大概的流程，这里我们详细的了解下具体的内容;
内容
这一块主要围绕init.ts中的initState进行剖析，初始化生命周期之后紧接着。
initState
代码语言：javascript复制
initState的方法位于scr/core/instance/state.ts中；
const sharedPropertyDefinition = {
enumerable: true,
configurable: true,
get: noop,
set: noop
}
export function proxy(target: Object, sourceKey: string, key: string) {
// get方法
sharedPropertyDefinition.get = function proxyGetter() {
return this[sourceKey][key]
}
// set方法
sharedPropertyDefinition.set = function proxySetter(val) {
this[sourceKey][key] = val
}
Object.defineProperty(target, key, sharedPropertyDefinition)
}
export function initState(vm: Component) {
const opts = vm.$options
// 存在props则初始化props
if (opts.props) initProps(vm, opts.props)
// Composition API
// 初始化组合式API
initSetup(vm)
// 存在方法则初始化方法
if (opts.methods) initMethods(vm, opts.methods)
// 存在data则初始化data
if (opts.data) {
initData(vm)
} else {
const ob = observe((vm._data = {}))
ob && ob.vmCount
}
// 存在计算属性则初始化计算属性
if (opts.computed) initComputed(vm, opts.computed)
// 存在监听且监听不等于nativeWatch（这个主要是针对火狐浏览器进行处理）则初始化监听
if (opts.watch && opts.watch !== nativeWatch) {
initWatch(vm, opts.watch)
}
}
function initProps(vm: Component, propsOptions: Object) {
const propsData = vm.$options.propsData || {}
const props = (vm._props = shallowReactive({}))
// cache prop keys so that future props updates can iterate using Array
// instead of dynamic object key enumeration.
// 缓存prop的keys以便将来更新props时可以使用数组代替动态的迭代对象key
const keys: string[] = (vm.$options._propKeys = [])
// 判断是否是根组件
const isRoot = !vm.$parent
// root instance props should be converted
if (!isRoot) {
// 如果不是根组件就关闭响应式处理,防止defineReactive做响应式处理
toggleObserving(false)
}
for (const key in propsOptions) {
keys.push(key)
// 对prop数据进行校验
const value = validateProp(key, propsOptions, propsData, vm)
/* istanbul ignore else */
if (__DEV__) {
const hyphenatedKey = hyphenate(key)
// 检查属性是否是保留属性
if (
isReservedAttribute(hyphenatedKey) ||
config.isReservedAttr(hyphenatedKey)
) {
warn(
`"${hyphenatedKey}" is a reserved attribute and cannot be used as component prop.`,
vm
)
}
defineReactive(props, key, value, () => {
if (!isRoot && !isUpdatingChildComponent) {
warn(
`Avoid mutating a prop directly since the value will be `
`overwritten whenever the parent component re-renders. `
`Instead, use a data or computed property based on the prop's `
`value. Prop being mutated: "${key}"`,
vm
)
}
})
} else {
defineReactive(props, key, value)
}
// static props are already proxied on the component's prototype
// during Vue.extend(). We only need to proxy props defined at
// instantiation here.
// 在Vue.extend（）过程中，静态props已经在组件的原型上被代理。我们只需要在这里实例化时代理定义的props。
if (!(key in vm)) {
proxy(vm, `_props`, key)
}
}
// 开启响应式处理
toggleObserving(true)
}
/**
* 初始化data
* @param vm
*/
function initData(vm: Component) {
let data: any = vm.$options.data
// 通过getData将函数转为对象
data = vm._data = isFunction(data) ? getData(data, vm) : data || {}
if (!isPlainObject(data)) {
data = {}
// https://v2.cn.vuejs.org/v2/guide/components.html#data-必须是一个函数
// 一个组件的 data 选项必须是一个函数，因此每个实例可以维护一份被返回对象的独立的拷贝
// 避免了实例之间相互影响
__DEV__ &&
warn(
'data functions should return an object:n'
'https://v2.vuejs.org/v2/guide/components.html#data-Must-Be-a-Function',
vm
)
}
// proxy data on instance
const keys = Object.keys(data)
const props = vm.$options.props
const methods = vm.$options.methods
let i = keys.length
while (i--) {
const key = keys[i]
// 检查key名是否在methods中已经使用
if (__DEV__) {
if (methods && hasOwn(methods, key)) {
warn(`Method "${key}" has already been defined as a data property.`, vm)
}
}
// 检查key名是否在props中使用
if (props && hasOwn(props, key)) {
__DEV__ &&
warn(
`The data property "${key}" is already declared as a prop. `
`Use prop default value instead.`,
vm
)
// 检查key名是否符合规范,即不以$和_开头
} else if (!isReserved(key)) {
// 代理数据 |本质上还是 Object.defineProperty
proxy(vm, `_data`, key)
}
}
// observe data | 响应式数据
const ob = observe(data)
ob && ob.vmCount
}
/**
* 获取data内容|转为对象
* @param data
* @param vm
* @returns
*/
export function getData(data: Function, vm: Component): any {
// #7573 disable dep collection when invoking data getters
pushTarget()
try {
return data.call(vm, vm)
} catch (e: any) {
handleError(e, vm, `data()`)
return {}
} finally {
popTarget()
}
}
const computedWatcherOptions = { lazy: true }
function initComputed(vm: Component, computed: Object) {
// $flow-disable-line
// 创建一个空对象
const watchers = (vm._computedWatchers = Object.create(null))
// computed properties are just getters during SSR
// 计算的内容只是SSR期间的getter
// 是否服务端渲染
const isSSR = isServerRendering()
for (const key in computed) {
const userDef = computed[key]
const getter = isFunction(userDef) ? userDef : userDef.get
if (__DEV__ && getter == null) {
warn(`Getter is missing for computed property "${key}".`, vm)
}
if (!isSSR) {
// create internal watcher for the computed property.
// 不是服务端渲染,就为计算属性创建内部观察程序。
// noop 空函数：function() {}
watchers[key] = new Watcher(
vm,
getter || noop,
noop,
computedWatcherOptions
)
}
// component-defined computed properties are already defined on the
// component prototype. We only need to define computed properties defined
// at instantiation here.
// 组件定义的计算内容已经在组件原型上定义。我们只需要在这里定义实例化时定义的计算内容。
if (!(key in vm)) {
defineComputed(vm, key, userDef)
} else if (__DEV__) {
// 开发环境下检查key名是否被过早的定义在data,props,methods中
if (key in vm.$data) {
warn(`The computed property "${key}" is already defined in data.`, vm)
} else if (vm.$options.props && key in vm.$options.props) {
warn(`The computed property "${key}" is already defined as a prop.`, vm)
} else if (vm.$options.methods && key in vm.$options.methods) {
warn(
`The computed property "${key}" is already defined as a method.`,
vm
)
}
}
}
}
export function defineComputed(
target: any,
key: string,
userDef: Record<string, any> | (() => any)
) {
// 是否服务端渲染
const shouldCache = !isServerRendering()
// 定义get和set
if (isFunction(userDef)) {
sharedPropertyDefinition.get = shouldCache
? createComputedGetter(key)
: createGetterInvoker(userDef)
sharedPropertyDefinition.set = noop
} else {
sharedPropertyDefinition.get = userDef.get
? shouldCache && userDef.cache !== false
? createComputedGetter(key)
: createGetterInvoker(userDef.get)
: noop
sharedPropertyDefinition.set = userDef.set || noop
}
if (__DEV__ && sharedPropertyDefinition.set === noop) {
sharedPropertyDefinition.set = function () {
warn(
`Computed property "${key}" was assigned to but it has no setter.`,
this
)
}
}
Object.defineProperty(target, key, sharedPropertyDefinition)
}
function createComputedGetter(key) {
return function computedGetter() {
const watcher = this._computedWatchers && this._computedWatchers[key]
if (watcher) {
// 是否被计算过,如果dirty为true表明未被计算过
if (watcher.dirty) {
watcher.evaluate() // 调用watcher.get方法,值会保存在watcher.value上
}
if (Dep.target) {
if (__DEV__ && Dep.target.onTrack) {
Dep.target.onTrack({
effect: Dep.target,
target: this,
type: TrackOpTypes.GET,
key
})
}
watcher.depend()
}
return watcher.value
}
}
}
function createGetterInvoker(fn) {
return function computedGetter() {
return fn.call(this, this)
}
}
function initMethods(vm: Component, methods: Object) {
const props = vm.$options.props
// 循环遍历methods
for (const key in methods) {
if (__DEV__) {
// 不是函数类型发出警告
if (typeof methods[key] !== 'function') {
warn(
`Method "${key}" has type "${typeof methods[
key
]}" in the component definition. `
`Did you reference the function correctly?`,
vm
)
}
// 函数名称和props中的是否冲突
if (props && hasOwn(props, key)) {
warn(`Method "${key}" has already been defined as a prop.`, vm)
}
// 函数名不能以_和$开头
if (key in vm && isReserved(key)) {
warn(
`Method "${key}" conflicts with an existing Vue instance method. `
`Avoid defining component methods that start with _ or $.`
)
}
}
// 将methods绑定在当前实例上
vm[key] = typeof methods[key] !== 'function' ? noop : bind(methods[key], vm)
}
}
function initWatch(vm: Component, watch: Object) {
// 遍历watch
for (const key in watch) {
const handler = watch[key]
// 是否是数组
if (isArray(handler)) {
// 循环创建watcher监听回调函数
for (let i = 0; i < handler.length; i ) {
createWatcher(vm, key, handler[i])
}
} else {
// 创建watcher监听回调函数
createWatcher(vm, key, handler)
}
}
}
function createWatcher(
vm: Component,
expOrFn: string | (() => any),
handler: any,
options?: Object
) {
// 检查是否是普通对象
if (isPlainObject(handler)) {
// 将handler挂载到options属性上
options = handler
// 提取handler属性赋值给handler
handler = handler.handler
}
// 是否是字符串
if (typeof handler === 'string') {
// 从实例中找到handler赋值给handler
handler = vm[handler]
}
// 实例上的$watch方法
return vm.$watch(expOrFn, handler, options)
}
