Event Rate Limiting (Rolling Window)

1type RateLimitEvent = { type: string; timestamp: number };
2
3function rateLimit(events: RateLimitEvent[], limit: number, windowMs: number): RateLimitEvent[] {
4    const queues = new Map<string, number[]>(); // type -> timestamps kept in window
5    const result: RateLimitEvent[] = [];
6
7    for (const e of events) {
8        const q = queues.get(e.type) ?? [];
9        queues.set(e.type, q);
10
11        const threshold = e.timestamp - windowMs;
12
13        // Remove expired timestamps from the front
14        while (q.length > 0 && q[0] < threshold) {
15            q.shift();
16        }
17
18        if (q.length < limit) {
19            q.push(e.timestamp);
20            result.push(e);
21        }
22        // else: drop it
23    }
24
25    return result;
26}
27
28const events: RateLimitEvent[] = [
29    { type: 'click', timestamp: 1000 },
30    { type: 'click', timestamp: 1001 },
31    { type: 'click', timestamp: 1002 },
32    { type: 'click', timestamp: 1003 },
33    { type: 'click', timestamp: 1004 },
34    { type: 'click', timestamp: 1005 },
35    { type: 'click', timestamp: 1006 },
36    { type: 'click', timestamp: 1007 },
37];
38
39const limitedEvents = rateLimit(events, 3, 5);
40console.log(limitedEvents);
41
42