Queue.js

/** Class representing a Queue. 
 * @constructor
*/

class Queue {

  constructor() {
    this._storage = {};
    this._length = 0;
    this._headIndex = 0;
  }
  /*
  * Enqueues a new value at the end of the queue
  * @param {*} value the value to enqueue
  */
  enqueue(value) {
    if(value !== ''){
      this._storage[this._headIndex + this._length] = value;
      this._length++;
    }
  }

  /*
  * Dequeues the value from the beginning of the queue and returns it
  * @return {*} the first and oldest value in the queue
  */
  dequeue() {
    if(!this.isEmpty()){
      const value = this._storage[this._headIndex];
      delete this._storage[this._headIndex];
      this._length--;
      this._headIndex++;
      return value;
    }
  }
  /*
  * Returns the value at the beginning of the queue without removing it from the queue
  * @return {*} the first and oldest value in the queue
  */
  peek() {
    if(!this.isEmpty()){
      return this._storage[this._headIndex];
    }
  }

  /*
  * Returns true if queue is empty else false
  */
  isEmpty(){
    return this._length === 0;
  }
}

let queue = new Queue();

queue.enqueue('zero');
queue.peek();
queue.dequeue();