Javascript Question posted in
A very good W3school tutorial can be found here.

Javascript – How to repeat RxJS from() but skip first emission

I have the following code which I expect should emit for each member in the scheduleEntries array, and each scheduleEntry should repeat forever, and I’m trying to get the first emission of each array member to be skipped. How can I get it to work?

Right now it doesn’t emit at all with skip(1)

import { Observable, from, mergeMap, of, repeat, skip, timer } from 'rxjs';

class Schedule {
  private scheduleEntries = [
    { value: true, countdown: 48395 },
    { value: true, countdown: 38395 },
    { value: false, countdown: 42394 },
    { value: true, countdown: 4835 },
  ];

  private lockEmitter$: Observable<ScheduleEntry>;

  constructor() {
    this.lockEmitter$ = from(this.scheduleEntries).pipe(
      skip(1), // skip the first emission for each entry
      mergeMap(entry => of(entry).pipe(
        repeat({ delay: () => this.delayedObservableFactory(entry) }),
      )),
    );
    this.lockEmitter$.subscribe(console.log);
  }

  private delayedObservableFactory(entry: ScheduleEntry) {
    return new Observable(observer => {
      timer(entry.countdown).subscribe(() => observer.next({}));
    });
  }
}


interface ScheduleEntry {
  value: boolean;
  countdown: number;
}
Tags:

2

Answers


  1. 0

    Think you need to move skip before pipe?

    Actually looking again skip is applying the whole array but you may need to skip each entry as your code comment suggests (missed that detail first time round)

      mergeMap(entry => of(entry).pipe(
    delay(entry.countdown),
    skip(1),
    repeat()
  )),
    Login or Signup to reply.
  2. 0

    When you use from, we require concatMap to ensure the items are executed in order, please find below stackblitz

    import './style.css';

import { rx, map } from 'rxjs';
import {
  Observable,
  from,
  mergeMap,
  of,
  repeat,
  skip,
  timer,
  delay,
} from 'rxjs';
import { concatMap } from 'rxjs/operators';

class Schedule {
  private scheduleEntries = [
    { value: true, countdown: 48395 },
    { value: true, countdown: 1000 },
    { value: false, countdown: 1000 },
    { value: true, countdown: 1000 },
  ];

  private lockEmitter$: Observable<ScheduleEntry>;

  constructor() {
    this.lockEmitter$ = from(this.scheduleEntries).pipe(
      skip(1),
      concatMap((item: ScheduleEntry) => of(item).pipe(delay(item.countdown))),
      repeat()
    );
    this.lockEmitter$.subscribe(console.log);
  }
}

new Schedule();

interface ScheduleEntry {
  value: boolean;
  countdown: number;
}

    stackblitz

    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search