code: function (value) {
          var node;
  
          if (value instanceof LinkedListNode) {
              node = value;
              validateNode(node, null);
  
              if (this.head === null) {
                  this.insertNodeToEmptyList(node);
              }
              else {
                  this.insertNodeBefore(this.head, node);
                  this.head = node;
              }
          }
          else {
              node = new LinkedListNode(value);
              this.addFirst(node);
          }
  
          return node;
      }
docs: Adds the specified new node at the start of the LinkedList.
  @param {LinkedListNode|Object} value The value or the LinkedListNode to add at the start of the LinkedList.
  @returns {LinkedListNode}