Subject 的其中一个变体就是 BehaviorSubject，它有一个“当前值”的概念。它保存了发送给消费者的最新值。并且当有新的观察者订阅时，会立即从 BehaviorSubject 那接收到“当前值”。
import { Component, OnInit } from '@angular/core';
import { BehaviorSubject } from 'rxjs/BehaviorSubject';
@Component({
selector: 'app-subject',
templateUrl: './subject.component.html',
styleUrls: ['./subject.component.css']
})
export class SubjectComponent implements OnInit {
constructor() { }
ngOnInit() {
const subject: BehaviorSubject<string> = new BehaviorSubject<string>('Leo');
subject.subscribe( // 观察者A订阅
(val: string) => {
console.log(`observerA: ${val}`);
}
);
subject.next('Raph');
subject.next('Mikey');
subject.subscribe( // 观察者B订阅
(val: string) => {
console.log(`observerB: ${val}`);
}
);
subject.next('Don');
}
}