Simple least-recently inserted cache.

lruCache.ts

export default class LeastRecentlyInsertedCache<T> implements Iterable<T> {
  private maxSize: number;

  // Set objects maintain insertion order, making them appropriate for keeping track of when values
  // are added relative to each other.
  private set = new Set<T>();

  constructor(maxSize: number) {
    this.maxSize = maxSize;
  }

  [Symbol.iterator]() {
    return this.set.values();
  }

  add(item: T) {
    // Ensure the item is placed at the end if the cache already contains it.
    this.set.delete(item);
    this.set.add(item);

    // Remove the first (i.e. oldest) value if adding a new one pushes the set beyond its max size.
    if (this.set.size > this.maxSize) {
      const firstValue = this.set.values().next().value;
      this.set.delete(firstValue);
    }
  }
}