constructor(capacity) {
        this.capacity = capacity;
        this.map = new Map();

        this.head = {};
        this.tail = {};

        this.head.next = this.tail;
        this.tail.prev = this.head;
    }
https://leetcode.com/problems/lru-cache/
Time O(1) | Space O(N)
Your LRUCache object will be instantiated and called as such:
var obj = new LRUCache(capacity)
var param_1 = obj.get(key)
obj.put(key,value)