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const obj = {
};

let val = 'cjg';
Object.defineProperty(obj, 'name', {
 get() {
 console.log('劫持了你的取值操作啦');
 return val;
 },
 set(newVal) {
 console.log('劫持了你的賦值操作啦');
 val = newVal;
 }
});

console.log(obj.name);
obj.name = 'cwc';
console.log(obj.name);

class Dep {
 constructor() {
 this.subs = [];
 }
 // 增加訂閱者
 addSub(sub) {
 if (this.subs.indexOf(sub) < 0) {
 this.subs.push(sub);
 }
 }
 // 通知訂閱者
 notify() {
 this.subs.forEach((sub) => {
 sub.update();
 })
 }
}

const dep = new Dep();

const sub = {
 update() {
 console.log('sub1 update')
 }
}

const sub1 = {
 update() {
 console.log('sub2 update');
 }
}

dep.addSub(sub);
dep.addSub(sub1);

class Observer {
 constructor(data) {
 // 如果不是對(duì)象，則返回
 if (!data || typeof data !== 'object') {
 return;
 }
 this.data = data;
 this.walk();
 }

 // 對(duì)傳入的數(shù)據(jù)進(jìn)行數(shù)據(jù)劫持
 walk() {
 for (let key in this.data) {
 this.defineReactive(this.data, key, this.data[key]);
 }
 }
 // 創(chuàng)建當(dāng)前屬性的一個(gè)發(fā)布實(shí)例，使用Object.defineProperty來對(duì)當(dāng)前屬性進(jìn)行數(shù)據(jù)劫持。
 defineReactive(obj, key, val) {
 // 創(chuàng)建當(dāng)前屬性的發(fā)布者
 const dep = new Dep();
 /*
 * 遞歸對(duì)子屬性的值進(jìn)行數(shù)據(jù)劫持，比如說對(duì)以下數(shù)據(jù)
 * let data = {
 * name: 'cjg',
 * obj: {
 * name: 'zht',
 * age: 22,
 * obj: {
 * name: 'cjg',
 * age: 22,
 * }
 * },
 * };
 * 我們先對(duì)data最外層的name和obj進(jìn)行數(shù)據(jù)劫持，之后再對(duì)obj對(duì)象的子屬性obj.name,obj.age, obj.obj進(jìn)行數(shù)據(jù)劫持，層層遞歸下去，直到所有的數(shù)據(jù)都完成了數(shù)據(jù)劫持工作。
 */
 new Observer(val);
 Object.defineProperty(obj, key, {
 get() {
 // 若當(dāng)前有對(duì)該屬性的依賴項(xiàng)，則將其加入到發(fā)布者的訂閱者隊(duì)列里
 if (Dep.target) {
  dep.addSub(Dep.target);
 }
 return val;
 },
 set(newVal) {
 if (val === newVal) {
  return;
 }
 val = newVal;
 new Observer(newVal);
 dep.notify();
 }
 })
 }
}

// 發(fā)布者,將依賴該屬性的watcher都加入subs數(shù)組，當(dāng)該屬性改變的時(shí)候，則調(diào)用所有依賴該屬性的watcher的更新函數(shù)，觸發(fā)更新。
class Dep {
 constructor() {
 this.subs = [];
 }

 addSub(sub) {
 if (this.subs.indexOf(sub) < 0) {
 this.subs.push(sub);
 }
 }

 notify() {
 this.subs.forEach((sub) => {
 sub.update();
 })
 }
}

Dep.target = null;

// 觀察者
class Watcher {
 /**
 *Creates an instance of Watcher.
 * @param {*} vm
 * @param {*} keys
 * @param {*} updateCb
 * @memberof Watcher
 */
 constructor(vm, keys, updateCb) {
 this.vm = vm;
 this.keys = keys;
 this.updateCb = updateCb;
 this.value = null;
 this.get();
 }

 // 根據(jù)vm和keys獲取到最新的觀察值
 get() {
 Dep.target = this;
 const keys = this.keys.split('.');
 let value = this.vm;
 keys.forEach(_key => {
 value = value[_key];
 });
 this.value = value;
 Dep.target = null;
 return this.value;
 }

 update() {
 const oldValue = this.value;
 const newValue = this.get();
 if (oldValue !== newValue) {
 this.updateCb(oldValue, newValue);
 }
 }
}

let data = {
 name: 'cjg',
 obj: {
 name: 'zht',
 },
};

new Observer(data);
// 監(jiān)聽data對(duì)象的name屬性，當(dāng)data.name發(fā)現(xiàn)變化的時(shí)候，觸發(fā)cb函數(shù)
new Watcher(data, 'name', (oldValue, newValue) => {
 console.log(oldValue, newValue);
})

data.name = 'zht';

// 監(jiān)聽data對(duì)象的obj.name屬性，當(dāng)data.obj.name發(fā)現(xiàn)變化的時(shí)候，觸發(fā)cb函數(shù)
new Watcher(data, 'obj.name', (oldValue, newValue) => {
 console.log(oldValue, newValue);
})

data.obj.name = 'cwc';
data.obj.name = 'dmh';