关于数据的依赖收集方面
以下是vue2的代码
export class Observer {
value: any;
dep: Dep;
vmCount: number; // number of vms that have this object as root $data
constructor (value: any) {
this.value = value
this.dep = new Dep()
this.vmCount = 0
def(value, '__ob__', this)
if (Array.isArray(value)) {
if (hasProto) {
protoAugment(value, arrayMethods)
} else {
copyAugment(value, arrayMethods, arrayKeys)
}
this.observeArray(value)
} else {
this.walk(value)
}
}
walk (obj: Object) {
const keys = Object.keys(obj)
for (let i = 0; i < keys.length; i++) {
defineReactive(obj, keys[i])
}
}
/**
* Observe a list of Array items.
*/
observeArray (items: Array<any>) {
for (let i = 0, l = items.length; i < l; i++) {
observe(items[i])
}
}
}
vue2当他new Vue的时候去对data里面的数据使用Object.defineProperty去做劫持getter和setter的时候,他是通过递归的方式去不停的给每个对象里面的key新增getter和setter,这样如果有那种深层次嵌套的对象就会让vue2的首屏性能变得很差
function createGetter(isReadonly = false, shallow = false) {
return function get(target: Target, key: string | symbol, receiver: object) {
if (key === ReactiveFlags.IS_REACTIVE) {
return !isReadonly
} else if (key === ReactiveFlags.IS_READONLY) {
return isReadonly
} else if (key === ReactiveFlags.IS_SHALLOW) {
return shallow
} else if (
key === ReactiveFlags.RAW &&
receiver ===
(isReadonly
? shallow
? shallowReadonlyMap
: readonlyMap
: shallow
? shallowReactiveMap
: reactiveMap
).get(target)
) {
return target
}
const targetIsArray = isArray(target)
if (!isReadonly && targetIsArray && hasOwn(arrayInstrumentations, key)) {
return Reflect.get(arrayInstrumentations, key, receiver)
}
const res = Reflect.get(target, key, receiver)
if (isSymbol(key) ? builtInSymbols.has(key) : isNonTrackableKeys(key)) {
return res
}
if (!isReadonly) {
track(target, TrackOpTypes.GET, key)
}
if (shallow) {
return res
}
if (isRef(res)) {
// ref unwrapping - skip unwrap for Array + integer key.
return targetIsArray && isIntegerKey(key) ? res : res.value
}
if (isObject(res)) {
// Convert returned value into a proxy as well. we do the isObject check
// here to avoid invalid value warning. Also need to lazy access readonly
// and reactive here to avoid circular dependency.
return isReadonly ? readonly(res) : reactive(res)
}
return res
}
}
以上是vue3的创建Proxy的代码,其中以下代码很好的解决了递归观察的问题
if (isObject(res)) {
return isReadonly ? readonly(res) : reactive(res)
}
他直接在getter里面去判断是否是对象的问题,然后再去进行递归,这样就不必第一次做观察的时候进行深度new Proxy,提升了首屏性能,并且优化了一些不必要的观察