框架
每个组件实例都会对应一个watcher实例，在组件渲染过程中把接触过的数据property记录为依赖。当依赖项的setter触发时，会通知watcher，重新渲染组件
vue实例中的data选项，在初始化时会遍历该对象所有属性，并使用Object.defineProperty转为getter/setter。
组件结构
Observer：主要是将对象转为响应式对象，在getter中，会创建Dep来收集依赖
Dep：用于存放watcher，即副作用函数effectFn
Watcher：观察者，当有数据更新时，会触发update
源码解析
在哪里绑定vue实例与watcher实例
在src/core/instance/lifecycle.ts中的mountComponent中
export function mountComponent(
vm: Component,
el: Element | null | undefined,
hydrating?: boolean
): Component {
vm.$el = el
callHook(vm, 'beforeMount')
let updateComponent
updateComponent = () => {
vm._update(vm._render(), hydrating)
}
const watcherOptions: WatcherOptions = {
before() {
if (vm._isMounted && !vm._isDestroyed) {
callHook(vm, 'beforeUpdate')
}
}
}
// we set this to vm._watcher inside the watcher's constructor
// since the watcher's initial patch may call $forceUpdate (e.g. inside child
// component's mounted hook), which relies on vm._watcher being already defined
new Watcher(
vm,
updateComponent,
noop,
watcherOptions,
true
)
hydrating = false
// flush buffer for flush: "pre" watchers queued in setup()
const preWatchers = vm._preWatchers
if (preWatchers) {
for (let i = 0; i < preWatchers.length; i++) {
preWatchers[i].run()
}
}
// manually mounted instance, call mounted on self
// mounted is called for render-created child components in its inserted hook
if (vm.$vnode == null) {
vm._isMounted = true
callHook(vm, 'mounted')
}
return vm
}vue实例中的data响应式初始化
在src/core/instance/state.ts/initData中，主要是observe(data)这个
function initData(vm: Component) {
let data: any = vm.$options.data
data = vm._data = isFunction(data) ? getData(data, vm) : data || {}
if (!isPlainObject(data)) {
data = {}
}
// proxy data on instance
const keys = Object.keys(data)
const props = vm.$options.props
const methods = vm.$options.methods
let i = keys.length
while (i--) {
const key = keys[i]
if (props && hasOwn(props, key)) {
} else if (!isReserved(key)) {
proxy(vm, `_data`, key)
}
}
// observe data
const ob = observe(data)
ob && ob.vmCount++
}对Object的变化监测
Observer只追踪数据是否被修改，无法追踪新增和删除属性
Vue提供了Vue.prototype.$set和Vue.prototype.$delete,内部也是调用Observer的方法
import {
set,
del
} from '../observer/index'
Vue.prototype.$set = set
Vue.prototype.$delete = del
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