LinkedList.prototype.append = function(data) {
  let newNode = new Node(data);
  let nodeToCheck = this.head;
  if(!nodeToCheck) {
    this.head = newNode;

    // increment the LinkedList's length
    this.length++;
    return newNode;
  } else {
    while(nodeToCheck.next) {
      nodeToCheck = nodeToCheck.next;
    }

    // once were at the end of the list
    nodeToCheck.next = newNode;

    // increment the LinkedList's length
    this.length++;
    return newNode;
  }
}