simple FIFO Queue javascript

function Queue(){
     var head = null;
     var curr = null;

     this.empty = function(){ if (head === null) return true; else return false;}
     this.push  = function(val){
                      if (head === null){
                head = { value : val, next : null };
                curr = head;
               } else {
                curr.next = { value : val, next : null };
                var tmp = curr.next;
                curr = tmp;
               }
             }

     this.top = function(){
                    if (head === null ) return null;
            else return head.value;
                     }

         this.pop = function(){
                    if(head !== null){
                  head = head.next;
            } else {
                  curr = null;
            }
                   }
  }