Vue变化检测Object使用DefineProperty、数组使用方法拦截实现。最近，Vue3.0将采用ES6 Proxy的形式重新实现Vue的变化检测，在官方还没给出新方法之前，我们先实现一个基于Proxy的变化检测。
模块划分
参照之前Vue变化检测的代码，将Vue 变化检测的功能分为以下几个部分。
首先，我们要确定的问题是，将Dep依赖搜集存在哪里。Vue 2.x里，Object的依赖收集放在defineRactive，Array的依收集存入到Observer中。ES6 Proxy里，考虑到让handler访问dep，我们将依赖放入到Observer中。
Observer
observer.js功能代码如下：
import Dep from './dep';import { isObject } from './utils';export default class Observer { constructor (value) { // 递归处理子元素 this.obeserve(value); // 实现当前元素的代理 this.value = this.proxyTarget(value); } proxyTarget (targetBefore, keyBefore) { const dep = new Dep(); targetBefore.__dep__ = dep; let self = this; const filtersAtrr = val => ['__dep__', '__parent__'].indexOf(val) > -1; return new Proxy(targetBefore, { get: function(target, key, receiver){ if (filtersAtrr(key)) return Reflect.get(target, key, receiver); if (!Array.isArray(target)) { dep.depend(key); } // sort/reverse等不改变数组长度的，在get里触发 if (Array.isArray(target)) { if ((key === 'sort' || key === 'reverse') && target.__parent__) { target.__parent__.__dep__.notify(keyBefore); } } return Reflect.get(target, key, receiver); }, set: function(target, key, value, receiver){ if (filtersAtrr(key)) return Reflect.set(target, key, value, receiver); // 新增元素，需要proxy const { newValue, isChanged } = self.addProxyTarget(value, target, key, self); // 设置key为新元素 Reflect.set(target, key, newValue, receiver); // notify self.depNotify(target, key, keyBefore, dep, isChanged); return true; }, }); } addProxyTarget(value, target, key, self) { let newValue = value; let isChanged = false; if (isObject(value) && !value.__parent__) { self.obeserve(newValue); newValue = self.proxyTarget(newValue, key); newValue.__parent__ = target; isChanged = true; } return { newValue, isChanged, } } depNotify(target, key, keyBefore, dep, isChanged) { if (isChanged && target.__parent__) { target.__parent__.__dep__.notify(keyBefore); return; } if (Array.isArray(target)) { if (key === 'length' && target.__parent__) { target.__parent__.__dep__.notify(keyBefore); } } else { dep.notify(key); } } obeserve(target) { // 只处理对象类型，包括数组、对象 if (!isObject(target)) return; for (let key in target) { if (isObject(target[key]) && target[key] !== null) { this.obeserve(target[key]); target[key] = this.proxyTarget(target[key], key); // 设置__parent__,方便子元素调用 target[key].__parent__ = target; } } }}在Observer中，针对对象，只需要执行 dep.depend(key) 、 dep.notify(key) 即可。添加 key 是为了能正确的触发收集，不知道怎么说明白为什么要这样做，只能一切尽在不言中了。
Array, 如何实现依赖的收集和触发那。依赖收集与Object类似， dep.depend(key) 完成数组的收集。关于触发，可以分为两个方面，一是改变数组长度、二未改变数组长度的。改变数组长度的，在set里，通过长度属性的设置触发父级元素的notify。为什么要使用父级元素的notify那？我们可以分析以下，在你设置数组的长度时，这时候的target/key/value分别是[]/length*, 这个时候，数组的依赖收集是没有的，你watcher的是数组，并不是数组本身。这个时候只能通过 target.__parent__.__dep__.notify(keyBefore) 触发父级的收集，完成数据变化的检测。二对于未改变数组长度的，这里的做法，虽然是直接 target.__parent__.__dep__.notify(keyBefore) 触发依赖，但是有个严重的问题，实际上更新的数据不是最新的，这个地方暂时还没想到比较好的方法，欢迎大家讨论。
Dep
Dep.js
let uid = 0;export default class Dep { constructor () { this.subs = {}; this.id = uid++; } addSub(prop, sub) { this.subs[prop] = this.subs[prop] || []; this.subs[prop].push(sub); } removeSub(prop, sub) { this.remove(this.subs[prop] || [], sub); } depend(prop) { if (Dep.target) { // 传入的是当前依赖 Dep.target.addDep(prop, this) } } notify(prop) { const subs = (this.subs[prop] || []).slice(); for (let i = 0, l = subs.length; i < l; i++) { subs[i].update(); } } remove(arr, item) { if (arr.length) { const index = arr.indexOf(item); if (index > -1) { return arr.splice(index, 1); } } }}Dep.target = nullconst targetStack = []export function pushTarget (_target) { if (Dep.target) targetStack.push(Dep.target) Dep.target = _target}export function popTarget () { Dep.target = targetStack.pop()}dep 添加prop实现类型的绑定，为什么要这么做那？使用proxy代理后，你假如wahcter对象下的几个元素，此时的deps将同时存在这几个元素，你触发依赖的时候，这些依赖都会执行。因此，通过key值绑定观察事件，触发时，能完成对象的正确触发。
watcher、utils
import { parsePath } from './utils';import { pushTarget, popTarget } from './dep'export default class Watcher { constructor(vm, expOrFn, cb) { // dep id集合 this.depIds = new Set(); this.vm = vm; this.getter = parsePath(expOrFn); this.cb = cb; this.value = this.get(); } get () { pushTarget(this); let value = this.getter.call(this.vm, this.vm); popTarget(); return value; } update() { const oldValue = this.value; this.value = this.get(); this.cb.call(this.vm, this.value, oldValue); } addDep (prop, dep) { const id = dep.id; if (!this.depIds.has(id)) { this.depIds.add(id); dep.addSub(prop, this); } }}utils.js
/** * 解析简单路径 */const bailRE = /[^/w.$]/;export function parsePath (path) { if (bailRE.test(path)) { return; } const segments = path.split('.'); return function (obj) { for (let i = 0; i < segments.length; i++) { if (!obj) return; obj = obj[segments[i]]; } return obj; };}/** * Define a property. */export function def (obj, key, val, enumerable) { Object.defineProperty(obj, key, { value: val, enumerable: !!enumerable, writable: true, configurable: true })}/** * Quick object check - this is primarily used to tell * Objects from primitive values when we know the value * is a JSON-compliant type. */export function isObject (obj) { return obj !== null && typeof obj === 'object'}/** * Check whether an object has the property. */const hasOwnProperty = Object.prototype.hasOwnPropertyexport function hasOwn (obj, key) { return hasOwnProperty.call(obj, key)}Utils.js/Watchers.js与Vue 2.x类似，这里就不多介绍了。
测试一下
test.js
import Observer from './observer';import Watcher from './watcher';let data = { name: 'lijincai', password: '***********', address: { home: '安徽亳州谯城区', }, list: [{ name: 'lijincai', password: 'you know it Object', }], };const newData = new Observer(data);let index = 0;const watcherName = new Watcher(newData, 'value.name', (newValue, oldValue) => { console.log(`${index++}: name newValue:`, newValue, ', oldValue:', oldValue);});const watcherPassword = new Watcher(newData, 'value.password', (newValue, oldValue) => { console.log(`${index++}: password newValue:`, newValue, ', oldValue:', oldValue);});const watcherAddress = new Watcher(newData, 'value.address', (newValue, oldValue) => { console.log(`${index++}: address newValue:`, newValue, ', oldValue:', oldValue);});const watcherAddressHome = new Watcher(newData, 'value.address.home', (newValue, oldValue) => { console.log(`${index++}: address.home newValue:`, newValue, ', oldValue:', oldValue);});const watcherAddProp = new Watcher(newData, 'value.addProp', (newValue, oldValue) => { console.log(`${index++}: addProp newValue:`, newValue, ', oldValue:', oldValue);});const watcherDataObject = new Watcher(newData, 'value.list', (newValue, oldValue) => { console.log(`${index++}: newValue:`, newValue, ', oldValue:', oldValue);});newData.value.name = 'resetName';newData.value.password = 'resetPassword';newData.value.name = 'hello world name';newData.value.password = 'hello world password';newData.value.address.home = 'hello home';newData.value.address.home = 'hello home2';newData.value.addProp = 'hello addProp';newData.value.addProp ={ name: 'ceshi',};newData.value.addProp.name = 'ceshi2';newData.value.list.push('1');newData.value.list.splice(0, 1);newData.value.list.sort();newData.value.list.reverse();newData.value.list.push('1');newData.value.list.unshift({name: 'nihao'});newData.value.list[0] = { name: 'lijincai', password: 'you know it Array',};newData.value.list[0].name = 'you know it array after';newData.value.list.pop();newData.value.list.shift();newData.value.list.length = 1;我们使用对象、数组测试一下我们的ES6 Proxy检测。
20:17:44.725 index.js?afc7:20 0: name newValue: resetName , oldValue: lijincai20:17:44.725 index.js?afc7:24 1: password newValue: resetPassword , oldValue: ***********20:17:44.725 index.js?afc7:20 2: name newValue: hello world name , oldValue: resetName20:17:44.725 index.js?afc7:24 3: password newValue: hello world password , oldValue: resetPassword20:17:44.726 index.js?afc7:32 4: address.home newValue: hello home , oldValue: 安徽亳州谯城区20:17:44.726 index.js?afc7:32 5: address.home newValue: hello home2 , oldValue: hello home20:17:44.726 index.js?afc7:36 6: addProp newValue: hello addProp , oldValue: undefined20:17:44.727 index.js?afc7:36 7: addProp newValue: Proxy {name: "ceshi", __dep__: Dep, __parent__: {…}} , oldValue: hello addProp20:17:44.727 index.js?afc7:40 0: newValue: Proxy {0: Proxy, 1: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: Proxy, 1: "1", __dep__: Dep, __parent__: {…}}20:17:44.728 index.js?afc7:40 1: newValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}}20:17:44.729 index.js?afc7:40 2: newValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}}20:17:44.731 index.js?afc7:40 3: newValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}}20:17:44.734 index.js?afc7:40 4: newValue: Proxy {0: "1", 1: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: "1", 1: "1", __dep__: Dep, __parent__: {…}}20:17:44.735 index.js?afc7:40 5: newValue: Proxy {0: Proxy, 1: "1", 2: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: Proxy, 1: "1", 2: "1", __dep__: Dep, __parent__: {…}}20:17:44.735 index.js?afc7:40 6: newValue: Proxy {0: Proxy, 1: "1", 2: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: Proxy, 1: "1", 2: "1", __dep__: Dep, __parent__: {…}}20:17:44.736 index.js?afc7:40 7: newValue: Proxy {0: Proxy, 1: "1", 2: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: Proxy, 1: "1", 2: "1", __dep__: Dep, __parent__: {…}}20:17:44.737 index.js?afc7:40 8: newValue: Proxy {0: Proxy, 1: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: Proxy, 1: "1", __dep__: Dep, __parent__: {…}}20:17:44.738 index.js?afc7:40 9: newValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}}20:17:44.738 index.js?afc7:40 10: newValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}}我们看到了ES6 Proxy后实现了Object/Array的检测，虽然还存在一些问题，但是基本的侦测变化的功能都已经具备了。
总结
以上所述是小编给大家介绍的ES6 Proxy实现Vue的变化检测问题,希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对武林网网站的支持！
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