Simple javascript cache

class CustomCache<T> {
  private cache: Map<
    string,
    {
      value: T;
      /** Timestamp in unix when the cache entry expires */
      expiry: number;
    }
  > = new Map();
  private cacheDuration: number;
  private maxCacheLength: number;

  private pruneExpiredEntries() {
    const now = Date.now();
    this.cache.forEach((value, key) => {
      if (value.expiry < now) {
        this.cache.delete(key);
      }
    });
  }

  /**
   * Creates a new CustomCache instance.
   * @param cacheDuration time in milliseconds for which the cache entry is valid
   * @param maxCacheLength maximum number of entries in the cache
   */
  constructor(cacheDuration: number = 1000, maxCacheLength: number = 1000) {
    this.maxCacheLength = maxCacheLength;
    this.cacheDuration = cacheDuration;
  }

  add(key: string, value: T) {
		if (this.cache.size >= this.maxCacheLength) {
			const firstKey = this.cache.keys().next().value;
			if (firstKey !== undefined) {
				this.cache.delete(firstKey);
			}
		}

		this.cache.set(key, {
			value,
			expiry: Date.now() + this.cacheDuration
		});
	}

  get(key: string): T | null {
    this.pruneExpiredEntries();
    return this.cache.get(key)?.value ?? null;
  }

  clear() {
    this.cache.clear();
  }
}

/*
 1000 = time in milliseconds for which the cache entry is valid
 100 = maximum number of entries in the cache
 */
const cache = new CustomCache<string>(1000, 100);

cache.add("test", "test");
console.log(cache.get("test"));
cache.clear();