ES6引入了一种新的原始数据类型（），表示独一无二的值，它是JavaScript语言的第七种数据类型.

A.function insert(newElement, item) { var newNode = new Node(newElement); var current = this.find(item); newNode.next = current.next; current.next = newNode; }
B.function display() { var currNode = this.head; while (!(currNode.next == null)) { print(currNode.next.element); currNode = currNode.next; } }   
C.function find(item) { var currNode = this.head; while (currNode.element != item) { currNode = currNode.next; }return currNode; }
D.以上都不对

A.next
B.prev
C.element
D.list

A.0 1 2 and 0 1 2
B.0 1 2 and 3 3 3
C.3 3 3 and 0 1 2
D.3 1 3 and 0 1 2