observable

对事件进行观察

class Event {
    constructor() {
      this.handlers = new Map();
    this.count = 0;
  }
  subscribe(handler) {
      this.handlers.set(++this.count, handler);
    return this.count;
  }
  unsubscribe(idx) {
      this.handlers.delete(idx);
  }
  // 1. 谁触发这个事件
  // 2. 额外的信息（事件参数）
  fire(sender, args) {
      this.handlers.forEach((handler) => {
        handler(sender, args);
    });
  }
}
class FallsIllArgs {
    constructor(address) {
      this.address = address;
  } 
}
class Person {
    constructor(name, address) {
    this.name = name;
      this.address = address;
    this.fallsIll= new Event();
  }
  catchCold() {
      this.fallsIll.fire(this, new FallsIllArgs(this.address));
  }
}
let person = new Person('张三', '游泳池');
let sub = person.fallsIll.subscribe((sender, args) => {
    console.log(`${sender.name}需要医生前往${args.address}`);
})
person.catchCold();
person.fallsIll.unsubscribe(sub);
person.catchCold();

对属性进行观察

class Event {
  constructor() {
    this.handlers = new Map();
    this.count = 0;
  }
  subscribe(handler) {
    this.handlers.set(++this.count, handler);
    return this.count;
  }
  unsubscribe(idx) {
    this.handlers.delete(idx);
  }
  fire(sender, args) {
    this.handlers.forEach((handler) => {
      handler(sender, args);
    });
  }
}
class PropertyChangedArgs {
  constructor(name, newValue) {
    this.name = name;
    this.newValue = newValue;
  }
}
class Person {
  constructor(age) {
    this._age = age;
    this.propertyChanged = new Event();
  }
  get age() {
    return this._age;
  }
  set age(value) {
    if (!value || this._age === value) {
      return;
    }
    this._age = value;
    this.propertyChanged.fire(this, new PropertyChangedArgs('age', value));
  }
}
class RegistrationChecker {
  constructor(person) {
    this.person = person;
    this.token = person.propertyChanged.subscribe(this.handleAgeChanged);
  }
  handleAgeChanged = (sender, args) => {
    console.log(args.name === 'arg');
    if (sender === this.person && args.name === 'age') {
      if (args.newValue < 18) {
        console.log(`很抱歉，您现在年龄还太小了，不能够注册`);
      } else {
        console.log(`现在可以开始注册了！`);
        sender.propertyChanged.unsubscribe(this.token);
      }
    }
  }
}
let person = new Person('Tom');
let checker = new RegistrationChecker(person);
for (let i = 15; i < 22; i++) {
  console.log(`年龄变到了${i}`);
  person.age = i;
}