An angular service providing a simple queue

queue-service.js

(function(){

    var app = angular.module('mcbQueue', [])
        .service('queue', [Queue]);
     /**
     *    Queue.js
     *
     *    A function to represent a queue
     *
     *    Created by Stephen Morley - http://code.stephenmorley.org/ - and released under
     *    the terms of the CC0 1.0 Universal legal code:
     *
     *    http://creativecommons.org/publicdomain/zero/1.0/legalcode
     *
     * 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 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) {
            queue.push(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);
        };
    }
})();