I'm working through Cracking the Coding Interview and I thought I'd implement all the data structures in JS 5. Can anyone explain to me why my toString method isn't working? 

Thanks!

```js
    function Node(data) {
     this.next = null;
      this.data = data;
    }

    Node.prototype.appendToTail = function(data) {
     var end = new Node(data);
      var n = this;
      while (n.next != null) {
       n = n.next;
      }
      n.next = end;
    }

    Node.prototype.toString = function(head) {

     console.log(head)

     if (head == null) {
       return ""
      } else {
       return head.data.toString() + "-> " + head.next.toString();
      }

    }

    var ll = new Node(1);
    ll.appendToTail(3);
    ll.appendToTail(4);

    console.log(ll.toString())
```