45Implement a retry() utility supporting maximum attempts and delays

Implement retry(fn, { attempts = 3, delay = 0, shouldRetry = () => true } = {}). It calls the async fn(attempt) (attempt numbers start at 1) and:

• resolves with the first successful result;
• after a failure, waits delay milliseconds and tries again, up to attempts calls in total;
• rejects with the last error when every attempt failed, or immediately when shouldRetry(error, attempt) returns false.

delay is a number, or a function (attempt) => ms for custom backoff.

const data = await retry(() => fetchJson("/api/report"), {
  attempts: 4,
  delay: (attempt) => 100 * 2 ** (attempt - 1), // 100, 200, 400 ms
  shouldRetry: (error) => error.status !== 400, // do not retry bad requests
});

Requirements

• Never call fn more than attempts times.
• No delay after the final failed attempt.
• A synchronous throw from fn counts as a failed attempt.
• attempts below 1 is treated as 1.