23. Promise Retry with Backoff

The promiseRetry function retries an asynchronous operation until it succeeds or the attempt limit is reached.

Implement promiseRetry(fn, options) where fn is a function that returns a Promise. If the promise rejects, retry it up to maxRetries total attempts.

The delay should follow exponential backoff:

delay = initialDelay * (backoffMultiplier ^ attempt)

If all attempts fail, reject with the last error. If any attempt succeeds, resolve with its result.

Options

{
  maxRetries: 3, // total number of attempts (including the first)
  initialDelay: 100,
  backoffMultiplier: 2
}

Example

let attempts = 0;

const fn = () => {
  attempts++;
  return attempts < 2
    ? Promise.reject('fail-' + attempts)
    : Promise.resolve('ok');
};

promiseRetry(fn, { maxRetries: 2, initialDelay: 10 })
  .catch(console.log); // 'fail-2'