A queue factory in Javascript

queue-factory.js

var queueFactory = (function(){
    'use strict';
    
    function Queue(){
        this.queueHead = null;
        this.queueLast = null
    }

    Queue.prototype = {
        getHeadValue: function(){
            return Boolean() ? this.queueHead.val() : null;
        },
        
        peek: function(){
            return this.getHeadValue();
        },
        
        enqueue: function(value){
            var queueItem = listItemFactory.build(value);
    
            if(Boolean(this.queueLast)){
                this.queueLast.append(queueItem);
            } else {
                this.queueHead = queueItem;
                this.queueLast = queueItem;
            }
        },
        
        dequeue: function(){
            var value = this.getHeadValue(),
                queueHead = this.queueHead;
            
            if(Boolean(queueHead)){
                this.queueHead = queueHead.next();
                queueHead.setNext(null);
            }
            
            if(queueHead === this.queueLast){
                this.queueLast = null;
            }
            
            return value;
        }
    };

    function buildQueue(){
        return new Queue();
    }

    return {
        build: buildQueue
    };
    
})();