Node.js: How do you implement a circuit breaker for database connections?

1class CircuitBreaker {
2    constructor(fn, options = {}) {
3        this.fn = fn;
4        this.state = "CLOSED";
5        this.failures = 0;
6        this.successes = 0;
7        this.threshold = options.threshold || 5;
8        this.timeout = options.timeout || 30000;
9        this.halfOpenAfter = options.halfOpenAfter || 5000;
10        this.nextAttempt = Date.now();
11    }
12
13    async call(...args) {
14        if (this.state === "OPEN") {
15            if (Date.now() < this.nextAttempt) {
16                throw new Error("Circuit breaker is OPEN");
17            }
18            this.state = "HALF_OPEN";
19        }
20
21        try {
22            const result = await Promise.race([
23                this.fn(...args),
24                new Promise((_, reject) =>
25                    setTimeout(() => reject(new Error("Timeout")), this.timeout)
26                ),
27            ]);
28            this.onSuccess();
29            return result;
30        } catch (err) {
31            this.onFailure();
32            throw err;
33        }
34    }
35
36    onSuccess() {
37        this.failures = 0;
38        this.state = "CLOSED";
39    }
40
41    onFailure() {
42        this.failures++;
43        if (this.failures >= this.threshold) {
44            this.state = "OPEN";
45            this.nextAttempt = Date.now() + this.halfOpenAfter;
46        }
47    }
48}
49
50// Usage
51const dbBreaker = new CircuitBreaker(
52    (query) => db.query(query),
53    { threshold: 5, timeout: 5000 }
54);
55
56try {
57    const result = await dbBreaker.call("SELECT * FROM users");
58} catch (err) {
59    // Return cached data or default
60}