function LinkedList(){
  this.head = null;
}
LinkedList.prototype.push = function(val){
    var node = {
       value: val,
       next: null
    }
    if(!this.head){
      this.head = node;
    }
    else{
      current = this.head;
      while(current.next){
        current = current.next;
      }
      current.next = node;
    }
  }

  var sll = new LinkedList();

//push node
sll.push(2);
sll.push(3);
sll.push(4);

//check values by traversing LinkedList
console.log(sll.head); //Object {data: 2, next: Object}
console.log(sll.head.next); //Object {data: 4, next: null}

console.log(sll.head.next.next); //Object {data: 4, next: null}