Classic LRU Cache in JavaScript. Goal: Real World Implementation

LRU Cache.js

function ListNode(key, value) {
    this.value = value
    this.key = key
    this.next = this.prev = null
}

/**
 * @param {number} capacity
 */
var LRUCache = function(capacity) {
    this.capacity = capacity
    this.size = 0
    this.head = new ListNode()
    this.tail = new ListNode()
    this.cache = new Map()
    this.head.next = this.tail
    this.tail.prev = this.head
}

/** 
 * @param {number} key
 * @return {number}
 */
LRUCache.prototype.get = function(key) {
    let node = this.cache.get(key)
    // console.log("===GET", key, this.cache, node)
    if(node) {
        this.moveToHead(node)
        return node.value
    } else {
        return -1
    }
};

LRUCache.prototype.moveToHead = function(node) {
  this.removeNode(node)
  this.addNode(node)
}

LRUCache.prototype.removeNode = function(node) {
  let prev = node.prev
  let next = node.next
  prev.next = next
  next.prev = prev    
  this.cache.delete(node.key)
  this.size --
}
    
LRUCache.prototype.addNode = function(node) {
    let next = this.head.next
    node.prev = this.head
    this.head.next = node
    node.next = next
    next.prev = node
    this.cache.set(node.key, node)    
    this.size ++ 
}

LRUCache.prototype.popTail = function() {
    let node = this.tail.prev
    this.removeNode(node)
}
/** 
 * @param {number} key 
 * @param {number} value
 * @return {void}
 */
LRUCache.prototype.put = function(key, value) {
    let node = this.cache.get(key)
    if(node) {
        node.value = value
        this.moveToHead(node)
    } else {
        this.addNode(new ListNode(key, value))
        if(this.size > this.capacity) {
            this.popTail()
        }
    }
};

/** 
 * 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)
 */