Simple LRU (Least Recently Used) cache implementation using TypeScript

lru.ts

interface LRUType<K, V> extends Iterable<[K, V]> {
  get(key: K): V | undefined;

  readonly size: number;

  set(key: K, value: V): LRUType<K, V>;

  delete(key): boolean;

  has(key): boolean;

  keys(): IterableIterator<K>;
}

class LRU<K, V> {
  max: number;
  cache: LRUType<K, V>;

  constructor(max: number) {
    this.max = max;
    this.cache = new Map<K, V>();
  }

  get(key: K): V {
    const item = this.cache.get(key);
    if (item) {
      this.cache.delete(key);
      this.cache.set(key, item);
    }

    return item;
  }

  set(key: K, value: V): void {
    if (this.cache.has(key)) {
      this.cache.delete(key);
    } else if (this.cache.size === this.max) {
      this.cache.delete(this.first());
    }

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

  first(): V {
    return this.cache.keys().next().value;
  }
}