细读Vue2.6.14 Core 源码(5): initState
/**
@date 2021-09-05
@description 细读Vue2.6.14 Core 源码(5): initState
*/
壹(序)
之前的章节走完了初始化(调用 created
钩子函数),在 beforeCreate
和 created
之间,有一步是调用 initState
, 这一步处理了 props
, methods
, data
, computed
, watch
, 至关重要,所以单独抽一章讲解。
贰(initState)
export function initState(vm: Component) {
vm._watchers = []
const opts = vm.$options
// 处理 props,设置为响应式并代理到 vm 实例
if (opts.props) initProps(vm, opts.props)
// 处理 methods
if (opts.methods) initMethods(vm, opts.methods)
// 处理 data
if (opts.data) {
initData(vm)
} else {
// new Vue 产生的实例会走这里
observe(vm._data = {}, true /* asRootData */)
}
// 处理 computed
if (opts.computed) initComputed(vm, opts.computed)
// 处理 watch
// 使用 createWatcher 函数($watch)处理
if (opts.watch && opts.watch !== nativeWatch) {
initWatch(vm, opts.watch)
}
}
叁(initProps)
function initProps(vm: Component, propsOptions: Object) {
// 获取 props data
const propsData = vm.$options.propsData || {}
// vm 声明 _props
const props = vm._props = {}
// 缓存 props 的 key,之后更新时直接使用,不需要重新获取,有利于性能
const keys = vm.$options._propKeys = []
// 是否是 root Vue 实例,也就是 new Vue 产生的实例
const isRoot = !vm.$parent
// root instance props should be converted
if (!isRoot) {
toggleObserving(false)
}
for (const key in propsOptions) {
// 缓存key
keys.push(key)
const value = validateProp(key, propsOptions, propsData, vm)
/* istanbul ignore else */
if (process.env.NODE_ENV !== 'production') {
// 转换 key 为 连字符样式(helloWorld => hello-world)
const hyphenatedKey = hyphenate(key)
// 检查是否是 Vue 保留字符(style, class, ref, scope...)
if (isReservedAttribute(hyphenatedKey) ||
config.isReservedAttr(hyphenatedKey)) {
warn(
`"${hyphenatedKey}" is a reserved attribute and cannot be used as component prop.`,
vm
)
}
// 响应式
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: "${key}"`,
vm
)
}
})
} else {
defineReactive(props, key, value)
}
// static props are already proxied on the component's prototype
// during Vue.extend(). We only need to proxy props defined at
// instantiation here.
if (!(key in vm)) {
// 代理 key 到 vm上
proxy(vm, `_props`, key)
}
}
toggleObserving(true)
}
肆(initMethods)
function initMethods(vm: Component, methods: Object) {
const props = vm.$options.props
for (const key in methods) {
// 非生产环境下的一些判断及报警告
// 阅读这些也是挺重要的,毕竟开发是在非生产环境下,看了这些能明白你控制台报的警告是为什么,从哪儿来
if (process.env.NODE_ENV !== 'production') {
// 是否是 function
if (typeof methods[key] !== 'function') {
warn(
`Method "${key}" has type "${typeof methods[key]}" in the component definition. ` +
`Did you reference the function correctly?`,
vm
)
}
// key 是不是 props 的属性
if (props && hasOwn(props, key)) {
warn(
`Method "${key}" has already been defined as a prop.`,
vm
)
}
// 检查 key 是否保留字段($/_)
if ((key in vm) && isReserved(key)) {
warn(
`Method "${key}" conflicts with an existing Vue instance method. ` +
`Avoid defining component methods that start with _ or $.`
)
}
}
// 放置在 vm 实例上
vm[key] = typeof methods[key] !== 'function' ? noop : bind(methods[key], vm)
}
}
伍(initData)
function initData(vm: Component) {
let data = vm.$options.data
// data 是一个 function还是一个 object
// 从这里可以看到,如果一个组件的 data 是 pure object 而不是通过 function 返回的话
// 那么所有复用此组件的地方,都是使用同一个 object,在 js 中,这样的情况不需多说
data = vm._data = typeof data === 'function'
? getData(data, vm)
: data || {}
// 不是 pure object,则重置为空对象
if (!isPlainObject(data)) {
data = {}
process.env.NODE_ENV !== 'production' && warn(
'data functions should return an object:\n' +
'https://vuejs.org/v2/guide/components.html#data-Must-Be-a-Function',
vm
)
}
// proxy data on instance
// data/props/methods 重复 key 的警告问题
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]
if (process.env.NODE_ENV !== 'production') {
// methods 中已经有当前 key
if (methods && hasOwn(methods, key)) {
warn(
`Method "${key}" has already been defined as a data property.`,
vm
)
}
}
// props 中已经有当前 key
if (props && hasOwn(props, key)) {
process.env.NODE_ENV !== 'production' && warn(
`The data property "${key}" is already declared as a prop. ` +
`Use prop default value instead.`,
vm
)
} else if (!isReserved(key)) {
// 代理 key 到 vm
proxy(vm, `_data`, key)
}
}
// observe data
observe(data, true /* asRootData */)
}
陆(initComputed)
function initComputed(vm: Component, computed: Object) {
// $flow-disable-line
// 初始化 watchers
const watchers = vm._computedWatchers = Object.create(null)
// computed properties are just getters during SSR
const isSSR = isServerRendering()
for (const key in computed) {
const userDef = computed[key]
// 获取 getter
const getter = typeof userDef === 'function' ? userDef : userDef.get
if (process.env.NODE_ENV !== 'production' && getter == null) {
warn(
`Getter is missing for computed property "${key}".`,
vm
)
}
if (!isSSR) {
// create internal watcher for the computed property.
// 创建 watcher
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.
// vm 实例上没有 [key] 属性
if (!(key in vm)) {
// 定义 computed,使用上面声明的 watcher
defineComputed(vm, key, userDef)
} else if (process.env.NODE_ENV !== 'production') {
// key 已存在的警告
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)
}
}
}
}
// defineComputed
export function defineComputed(
target: any,
key: string,
userDef: Object | Function
) {
const shouldCache = !isServerRendering()
// 生成 getter 和 setter
if (typeof userDef === 'function') {
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 (process.env.NODE_ENV !== 'production' &&
sharedPropertyDefinition.set === noop) {
sharedPropertyDefinition.set = function () {
warn(
`Computed property "${key}" was assigned to but it has no setter.`,
this
)
}
}
// 拦截
Object.defineProperty(target, key, sharedPropertyDefinition)
}
// createComputedGetter
function createComputedGetter(key) {
return function computedGetter() {
const watcher = this._computedWatchers && this._computedWatchers[key]
if (watcher) {
if (watcher.dirty) {
// 由于 computed 是懒加载,所以此时才去调用 watcher 的 get 函数
// 并且会将 dirty 设置为false
// 在调用 update 时又会重新设置为 true
// dirty 的作用就是 computed 的缓存功能,在一次更新中,只需要计算一次
watcher.evaluate()
}
if (Dep.target) {
// 依赖收集
watcher.depend()
}
return watcher.value
}
}
}
终(导航)
细读Vue2.6.14 Core 源码(2): After Vue
细读Vue2.6.14 Core 源码(3): initGlobalAPI
细读Vue2.6.14 Core 源码(5): initState
细读Vue2.6.14 Core 源码(6): defineReactive