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Sliding Window Rate Limiter (JavaScript)

Track request timestamps in a sliding window to count how many calls happened in the last interval, rejecting requests that exceed the allowed rate.

JavascriptResilience

Code

snippet
export function createRateLimiter({ limit, windowMs }) {
  if (!Number.isInteger(limit) || limit <= 0) {
    throw new RangeError("limit must be a positive integer");
  }
  const hits = [];
  return function allow(now = Date.now()) {
    const cutoff = now - windowMs;
    while (hits.length > 0 && hits[0] <= cutoff) hits.shift();
    if (hits.length >= limit) {
      return { allowed: false, retryAfterMs: hits[0] + windowMs - now };
    }
    hits.push(now);
    return { allowed: true, remaining: limit - hits.length };
  };
}

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