backoff

Problem

You need exponential backoff delays for a retry loop — doubling the wait on each failure up to a configurable maximum.

Solution

Use backoff(attempt, maxMs?) to compute min(1000 × 2^attempt, maxMs). Multiply by Math.random() for full-jitter.

import { backoff, retry } from '@vielzeug/arsenal';

const data = await retry((signal) => fetch('/api/data', { signal }).then((r) => r.json()), {
  times: 5,
  delay: (failureIndex) => backoff(failureIndex) * Math.random(),
  //              0: ~500ms, 1: ~1s, 2: ~2s, 3: ~4s (capped at 30s default)
});

Standalone

import { backoff } from '@vielzeug/arsenal';

backoff(0); // 1000
backoff(1); // 2000
backoff(2); // 4000
backoff(3, 5_000); // 5000 — capped at maxMs

Pitfalls

• Returns a deterministic value — add * Math.random() for jitter to avoid thundering herd.
• attempt is 0-based: backoff(0) = 1000 ms (1 second).

Related

• retry
• sleep