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A function to represent a queue

Created by Kate Morley - - and released under the terms
of the CC0 1.0 Universal legal code:


/* Creates a new queue. A queue is a first-in-first-out (FIFO) data structure -
 * items are added to the end of the queue and removed from the front.
function Queue(){

  // initialise the queue and offset
  var queue  = [];
  var offset = 0;
  // Returns the the queue.
  this.get = function(){
    return queue;
  // Returns the length of the queue.
  this.getLength = function(){
    return (queue.length - offset);

  // Returns true if the queue is empty, and false otherwise.
  this.isEmpty = function(){
    return (queue.length == 0);

  /* Enqueues the specified item. The parameter is:
   * item - the item to enqueue
  this.enqueue = function(item){

  /* Dequeues an item and returns it. If the queue is empty, the value
   * 'undefined' is returned.
  this.dequeue = function(){

    // if the queue is empty, return immediately
    if (queue.length == 0) return undefined;

    // store the item at the front of the queue
    var item = queue[offset];

    // increment the offset and remove the free space if necessary
    if (++ offset * 2 >= queue.length){
      queue  = queue.slice(offset);
      offset = 0;

    // return the dequeued item
    return item;


  /* Returns the item at the front of the queue (without dequeuing it). If the
   * queue is empty then undefined is returned.
  this.peek = function(){
    return (queue.length > 0 ? queue[offset] : undefined);

// create a new queue
var queue = new Queue();

// enqueue an item
// dequeue an item
var item = queue.dequeue();