rate limiting и retries/backoff: пример кода

// Production-grade fetch with retry, full jitter, Retry-After, and a cap.
async function fetchRetry(url, opts = {}, { retries = 4, base = 300, cap = 10_000 } = {}) {
  for (let attempt = 0; ; attempt++) {
    try {
      const res = await fetch(url, opts);
      // Retry only server errors + throttling. 4xx (except 429) is terminal.
      if (res.status === 429 || (res.status >= 500 && res.status !== 501)) {
        if (attempt >= retries) return res;              // give up, surface it
        const ra = res.headers.get('Retry-After');
        await sleep(ra ? retryAfterMs(ra)                // server told us when
                       : jitter(base, cap, attempt));    // else full jitter backoff
        continue;
      }
      return res;                                        // success or terminal 4xx
    } catch (err) {                                       // network error / timeout
      if (attempt >= retries) throw err;
      await sleep(jitter(base, cap, attempt));
    }
  }
}

// Full jitter: sleep a RANDOM amount up to the exponential ceiling.
const jitter = (base, cap, attempt) =>
  Math.random() * Math.min(cap, base * 2 ** attempt);

const sleep = (ms) => new Promise((r) => setTimeout(r, ms));

// Pace yourself PROACTIVELY off RateLimit headers instead of waiting to be 429'd.
const remaining = Number(res.headers.get('RateLimit-Remaining'));
const resetMs = Number(res.headers.get('RateLimit-Reset')) * 1000;
if (remaining < 5) await sleep(resetMs - Date.now()); // slow down before the wall