Implementing the Circuit Breaker Pattern in TypeScript (2026 Guide)

#backend #typescript #architecture #reliability

Your payment service is down. Every request to it times out after 30 seconds. 100 requests per second means 3000 threads waiting on a dead service. Your entire system cascades.

Three States

Closed = normal, requests pass. Open = failing, reject immediately. Half-Open = testing recovery with one probe.

Implementation

type State = "closed" | "open" | "half-open";
class CircuitBreaker {
  private state: State = "closed";
  private failures = 0;
  private lastFailure = 0;

  constructor(private threshold = 5, private timeout = 60000) {}
  async call(fn) {
    if (this.state === "open") {
      if (Date.now() - this.lastFailure > this.timeout) this.state = "half-open";
      else throw new Error("Circuit is OPEN");
    }
    try {
      const result = await fn();
      this.reset();
      return result;
    } catch (err) { this.recordFailure(); throw err; }
  }
  private reset() { this.state = "closed"; this.failures = 0; }
  private recordFailure() { this.failures++; this.lastFailure = Date.now();
    if (this.failures >= this.threshold) this.state = "open";
  }
}

Usage

const paymentBreaker = new CircuitBreaker(5, 60000);
app.post("/charge", async (req, res) => {
  try {
    const result = await paymentBreaker.call(() => stripe.charges.create(req.body));
    res.json(result);
  } catch (err) { res.status(503).json({ error: "Service unavailable" }); }
});

When to Trip the Circuit

Trip on: timeouts, 5xx responses, connection refused. Do NOT trip on: 4xx responses (client errors), validation failures.

Monitoring

Log every state transition. Alert on open circuits. Track: failure rate, trip count, recovery time.

Part of my Production Backend Patterns series. Follow for more practical backend engineering.

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