backoff-rxjs/src/observable/intervalBackoff.ts

A collection of helpful RxJS operators to deal with backoff strategies (like exponential backoff)

import { Observable, of, timer, SchedulerLike, asyncScheduler, expand, mapTo } from 'rxjs';
import { exponentialBackoffDelay, getDelay } from '../utils';

export interface IntervalBackoffConfig {
  initialInterval: number;
  maxInterval?: number;
  backoffDelay?: (iteration: number, initialInterval: number) => number;
}
/**
 * Creates an Observable that emits sequential numbers with by default
 * exponentially increasing interval of time.
 */
export function intervalBackoff(
  config: number | IntervalBackoffConfig,
  scheduler: SchedulerLike = asyncScheduler
): Observable<number> {
  let {
    initialInterval,
    maxInterval = Infinity,
    backoffDelay = exponentialBackoffDelay,
  } = typeof config === 'number' ? { initialInterval: config } : config;
  initialInterval = initialInterval < 0 ? 0 : initialInterval;
  return of(0, scheduler).pipe(
    // Expend starts with number 1 and then recursively
    // projects each value to new Observable and puts it back in.
    expand((iteration: number) =>
      timer(getDelay(backoffDelay(iteration, initialInterval), maxInterval))
        // Once timer is complete, iteration is increased
        .pipe(mapTo(iteration + 1))
    )
  );
}