switchMap is mergeMap that checks for an "inner" subscription. If the "inner" subscription exists, switchMap unsubscribes from that "inner" subscription which effectively "cancels" any pending pushes.
import { fromEvent, of, Subscriber } from "rxjs"import { ?scan, ?delay, ?mergeMap, ?switchMap} from "rxjs/operators"class MySwitchMapSubscriber extends Subscriber { ?innerSubscription ?constructor(sub, fn) { ???super(sub) ???this.fn = fn ?} ?_next(value) { ???console.log(`outer`, value) ???const o$ = this.fn(value) ???if (this.innerSubscription) { ?????this.innerSubscription.unsubscribe() ???} ???this.innerSubscription = o$.subscribe({ ?????next: value => { ???????console.log(` ?inner`, value) ???????this.destination.next(value) ?????} ???}) ?}}const mySwitchMap = fn => source => ?source.lift({ ???call(sub, source) { ?????source.subscribe( ???????new MySwitchMapSubscriber(sub, fn) ?????) ???} ?})const observable$ = fromEvent( ?document, ?"click").pipe( ?scan(i => i + 1, 0), ?mySwitchMap(value => of(value).pipe(delay(500))))const subscriber = { ?next: value => { ???console.log(value) ?}, ?complete: () => { ???console.log("done") ?}, ?error: value => { ???console.log(value) ?}}observable$.subscribe(subscriber)[RxJS] Implement RxJS `switchMap` by Canceling Inner Subscriptions as Values are Passed Through
原文地址：https://www.cnblogs.com/Answer1215/p/9715065.html