1. Rxjs helpful functions

// retry.ts
import { Observable } from 'rxjs/Observable';
import { delay, retryWhen, scan } from 'rxjs/operators';

export function retry<T>(count: number, wait: number): (source: Observable<T>) => Observable<T> {
  return retryWhen((errors) =>
    errors.pipe(
      // Each time an error occurs, increment the accumulator.
      // When the maximum number of retries have been attempted, throw the error.
      scan((acc, error) => {
        if (acc >= count) {
          throw error;
        }
        return acc + 1;
      }, 0),
      // Wait the specified number of milliseconds between retries.
      delay(wait),
    ),
  );
}

// demo
import { ajax } from 'rxjs/observable/dom/ajax';
import { of } from 'rxjs/observable/of';
import { catchError, map } from 'rxjs/operators';
import { retry } from './retry';

const name = ajax
  .getJSON<{ name: string }>('/api/employees/alice')
  .let(retry(3, 1000))
  .map((employee) => employee.name)
  .catch((error) => of(null));

// OR

const name = ajax
  .getJSON<{ name: string }>('/api/employees/alice')
  .pipe(retry(3, 1000), map((employee) => employee.name), catchError((error) => of(null)));

1.1. The rule combination to use to enforce a lettable-operator-only policy would be:

https://github.com/ReactiveX/rxjs-tslint:

// tslint.json
{
  "rulesDirectory": ["node_modules/rxjs-tslint"],
  "rules": {
    "rxjs-collapse-imports": true,
    "rxjs-pipeable-operators-only": true,
    "rxjs-no-static-observable-methods": true,
    "rxjs-proper-imports": true
  }
}