Exponential backoff retry - example with fake service

app.component.ts

// Determine if the error matches our expected type
// http://www.typescriptlang.org/docs/handbook/advanced-types.html#user-defined-type-guards
function isHttpError(error: {}): error is HttpError {
  // This is a type guard for interface
  // if HttpError was a class we would use instanceof check instead 
  return (error as HttpError).status !== undefined;
}

message$ = of('Call me!').pipe(
    tap(console.log),
    switchMap(() => this.service.callBackend()),
    retryBackoff({
      initialInterval: INIT_INTERVAL_MS,
      maxInterval: MAX_INTERVAL_MS,
      shouldRetry: (error) => {
        // error could be anything, including HttpError that 
        // we want to handle from sevice.callBackend()
        if (isHttpError(error)) {
          // If this is HttpError and status is not 404
          // then continue retrying
          return error.status !== '404';
        }
        // should retry for the rest of the types of errors.
        return true;
      },
    }),
)