Expiring Cache

interface CacheEntry<T> {
  value: T;
  expiresAt: number;
}

class ExpiringCache<T> {
  private readonly entries = new Map<string, CacheEntry<T>>();

  set(key: string, value: T, ttlMilliseconds: number): void {
    this.entries.set(key, {
      value,
      expiresAt: Date.now() + ttlMilliseconds,
    });
  }

  get(key: string): T | undefined {
    const entry = this.entries.get(key);

    if (!entry) {
      return undefined;
    }

    if (entry.expiresAt <= Date.now()) {
      this.entries.delete(key);
      return undefined;
    }

    return entry.value;
  }

  keys(): string[] {
    return [...this.entries.keys()].filter((key) => this.get(key) !== undefined);
  }
}

const cache = new ExpiringCache<number>();
cache.set("answer", 42, 60_000);
cache.set("score", 95, 60_000);

console.log(cache.get("answer"));
console.log(cache.keys());