JavaScript implementation of Queue Data Structure

queue.js

// Implement a Queue using LinkedLists
// we know that queue is LIFO
// operations: enqueue, dequeue

function QueueNode(val) {
  this.val = val;
  this.next = null;
}

function Queue() {
  this.head = null;
  this.tail = null;
}

Queue.prototype.enqueue = function(val) {
  var node = new QueueNode(val);
  
  if (this.head == null && this.tail == null) {
    this.head = node;
    this.tail = node;
  } else {
    if (this.tail !== null) {
      this.tail.next = node;
      this.tail = node;
    } else {
      this.tail = node;
    }
  }
};

Queue.prototype.dequeue = function() {
  var node = this.head;
  
  if (node !== null) {
    this.head = this.head.next;
    return node.val;
  }
  
  return null;
};

var queue = new Queue();

queue.enqueue(5);
queue.enqueue(6);
queue.enqueue(7);

console.log(queue.dequeue());
console.log(queue.dequeue());
console.log(queue.dequeue());
console.log(queue.dequeue());