A higher-order fetch that retry on error

onErrorRetryHOF.js

import Rx from "rxjs";

const MAX_RETRY = 3
const RETRY_DELAY = 500
export const onErrorRetryHOF = fetch => (input, init) => {
  let count = 0;
  return Rx.Observable.defer(() =>
    Rx.Observable.fromPromise(
      fetch(input, init).then(resp => {
        if ((resp.status + "").startsWith("5")) throw resp;
        return resp;
      })
    )
  )
    .retryWhen(errors => {
      return errors.mergeMap(error => {
        if (++count >= MAX_RETRY) {
          return Rx.Observable.throw(error);
        } else {
          return Rx.Observable.of(error).delay(RETRY_DELAY);
        }
      });
    })
    .toPromise()
    .then(
      resp => resp,
      resp => {
        if (resp.status === 500) return resp;
        throw resp;
      }
    );
};