Build Your Own Operators Easily | RxJS

operator.js

import { interval } from 'rxjs/observable/interval';
import { map, take, toArray } from 'rxjs/operators';

/**
 * an operator that takes every Nth value
 */
const takeEveryNth = (n: number) => <T>(source: Observable<T>) =>
  new Observable(observer => {
    let count = 0;
    return source.subscribe({
      next(x) {
        if (count++ % n === 0) observer.next(x);
      },
      error(err) { observer.error(err); },
      complete() { observer.complete(); }
    })
  });


interval(1000).pipe(
  takeEveryNth(2),
  map(x => x + x),
  takeEveryNth(3),
  take(3),
  toArray()
)
.subscribe(x => console.log(x));
// [0, 12, 24]