LRU cache as a JS Map

LRUMap.ts

class LRUMap<TKey, TValue> extends Map<TKey, TValue> {
  constructor(max: number) {
    super()
    const get = this.get.bind(this)
    const set = this.set.bind(this)
    this.get = (key: TKey) => {
      const item = get(key)
      if (item !== undefined) {
        // refresh key
        this.delete(key)
        set(key, item)
      }
      return item
    }
    this.set = (key: TKey, val: TValue) => {
      // refresh key
      if (this.has(key)) this.delete(key)
      // evict oldest
      else if (this.size == max) this.delete(this.keys().next().value!)
      set(key, val)
      return this
    }
  }
}