~~~
// 主题，接收状态变化，触发每个观察者
class Subject {
constructor() {
this.state = 0
this.observers = []
}
getState() {
return this.state
}
setState(state) {
this.state = state
this.notifyAllObservers()
}
attach(observer) {
this.observers.push(observer)
}
notifyAllObservers() {
this.observers.forEach(observer => {
observer.update()
})
}
}
// 观察者，等待被触发
class Observer {
constructor(name, subject) {
this.name = name
this.subject = subject
this.subject.attach(this)
}
update() {
console.log(`${this.name} update, state: ${this.subject.getState()}`)
}
}
// 测试代码
let s = new Subject()
let o1 = new Observer('o1', s)
let o2 = new Observer('o2', s)
let o3 = new Observer('o3', s)
s.setState(1)
s.setState(2)
s.setState(3)
~~~
