LRU Cache in Typescript

lru-cache.ts

class LRUCache<K, V> {
  private cache: Map<K, V>;
  private capacity: number;

  constructor(capacity: number) {
    this.capacity = capacity;
    this.cache = new Map();
  }

  /**
   * Get a value from the cache
   * Marks the key as recently used by moving it to the end
   */
  get(key: K): V | undefined {
    if (!this.cache.has(key)) {
      return undefined;
    }

    const value = this.cache.get(key)!;
    this.cache.delete(key);
    this.cache.set(key, value);

    return value;
  }

  /**
   * Put a value in the cache
   * If at capacity, evicts the least recently used item
   */
  put(key: K, value: V): void {
    if (this.cache.has(key)) {
      this.cache.delete(key);
    }

    else if (this.cache.size >= this.capacity) {
      const firstKey = this.cache.keys().next().value;

      this.cache.delete(firstKey);
    }

    this.cache.set(key, value);
  }

  /**
   * Check if key exists in cache
   */
  has(key: K): boolean {
    return this.cache.has(key);
  }

  /**
   * Get current size
   */
  size(): number {
    return this.cache.size;
  }

  /**
   * Display current cache state (in order from least to most recent)
   */
  display(): void {
    const items = Array.from(this.cache.entries())
      .map(([k, v]) => `${k}: ${v}`)
      .join(', ');
  }
}

// DEMO //
//
// Create cache with capacity of 3
const cache = new LRUCache<string, string>(3);

console.log('1. Adding items to cache (capacity: 3)');
cache.put('user:1', 'Alice');
cache.display(); // [user:1: Alice]

cache.put('user:2', 'Bob');
cache.display(); // [user:1: Alice, user:2: Bob]

cache.put('user:3', 'Charlie');
cache.display(); // [user:1: Alice, user:2: Bob, user:3: Charlie]

console.log('\n2. Cache is full. Adding new item will evict LRU (user:1)');
cache.put('user:4', 'David');
cache.display(); // [user:2: Bob, user:3: Charlie, user:4: David]

console.log('\n3. Accessing user:2 makes it most recently used');
console.log(`Get user:2 = ${cache.get('user:2')}`);
cache.display(); // [user:3: Charlie, user:4: David, user:2: Bob]

console.log('\n4. Adding user:5 will now evict user:3 (new LRU)');
cache.put('user:5', 'Eve');
cache.display(); // [user:4: David, user:2: Bob, user:5: Eve]

console.log('\n5. Accessing user:4 and then adding user:6');
console.log(`Get user:4 = ${cache.get('user:4')}`);
cache.display(); // [user:2: Bob, user:5: Eve, user:4: David]

cache.put('user:6', 'Frank');
cache.display(); // [user:5: Eve, user:4: David, user:6: Frank]

console.log('\n6. Updating existing key (user:5) moves it to most recent');
cache.put('user:5', 'Eve Updated');
cache.display(); // [user:4: David, user:6: Frank, user:5: Eve Updated]