在RxJS中组合不同种类的可观测项，但只发射来自其中一个的值

Question

我有一个行为主题和两个事件发射器。每当BehaviorSubject发出新值或任一EventEmitter发出事件时，我需要创建一个Observable，它返回BehaviorSubject的最新值。基本上，我并不关心EventEmitter发出的事件的值，它们应该只是一个触发器，以推出BehaviorSubject的最新值。

下面是一个例子：

import Rx from 'rxjs';
import {map} from 'rxjs/operators'
import {EventEmitter} from '@angular/core'

const bSubject = new Rx.BehaviorSubject('value1');
const emitter1 = new EventEmitter();
const emitter2 = new EventEmitter();

// Should I be using something othere than merge to create the Observable?
// Is merge ok but I should be using a special operator?
const myOberservable = Rx.merge(bSubject, emitter1, emitter2)

myOberservable.subscribe({next: value => console.log(value)});

emitter1.emit('event1');
bSubject.next('value2');
emitter2.emit('event2');
bSubject.next('value3');

/**
 * It prints:
 *  value1
 *  event1
 *  value2
 *  event2
 *  value3
 * 
 * But I want it to print:
 *  value1
 *  value1
 *  value2
 *  value2
 *  value3
 */

Answer 1

组合merge、WithLatestFrom和Map。顺便说一句，我已经更新了代码片段，以启用树摇动。

import { merge, BehaviorSubject } from 'rxjs';
import { withLatestFrom, map } from 'rxjs/operators'
import {EventEmitter} from '@angular/core'

const bSubject = new BehaviorSubject('value1');
const emitter1 = new EventEmitter();
const emitter2 = new EventEmitter();

const merged = merge(bSubject, emitter1, emitter2);
const myOberservable = merged.pipe(withLatestFrom(bSubject), map(x => x[1]));

myOberservable.subscribe({ next: value => console.log(value) });

emitter1.emit('event1');
bSubject.next('value2');
emitter2.emit('event2');
bSubject.next('value3');