```js
function LinkedList() {
  var length = 0;
  var head = null;
  var Node = function(element){
    this.element = element;
    this.next = null;
  };
  this.size = function(){
    return length;
  };
  this.head = function(){
    return head;
  };
  this.add = function(element){
    var node = new Node(element);
    if (head === null){
        head = node;
    } else {
      var currentNode = head;
      while (currentNode.next) {
        currentNode = currentNode.next;
      }
      currentNode.next = node;
    }
    length++;
  };
  // Only change code below this line
  // Only change code above this line
}
```
## Solution