Create a stack with a Queue

create_a_stack_with_queue.js

var Node = function(data){
        this.data = data;
        this.next = null;
};

var Queue = function(){
    this.head = null;
    this.tail = null;
}
Queue.prototype.add = function(x) {
    let node = new Node(x);
    if(this.tail) this.tail.next = node;
    if(this.head == null) this.head = node;
    this.tail = node;
}

Queue.prototype.remove = function() {
    let data = this.tail.data;
    
    if(this.head == this.tail){
        this.head = null;
        this.tail = null;
        return data;
    }
    
    let current = this.head;
    let previous = null;
    while(current.next != null){
        previous = current;
        current = current.next;
        this.tail = previous;
    }
    this.tail.next = null;
    return data;
}

var MyStack = function() {
    this.queue = new Queue();
};

/** 
 * @param {number} x
 * @return {void}
 */
MyStack.prototype.push = function(x) {
    this.queue.add(x);
};

/**
 * @return {number}
 */
MyStack.prototype.pop = function() {
    let data =  this.queue.remove();
    return data;
};

/**
 * @return {number}
 */
MyStack.prototype.top = function() {
    if(this.queue.tail == null) return;
    let data = this.queue.tail.data;
    return data;
};

/**
 * @return {boolean}
 */
MyStack.prototype.empty = function() {
    return (this.queue.head == null)
};