LC 206. Reverse Linked List

 1/**
 2 * Definition for singly-linked list.
 3 * function ListNode(val, next) {
 4 *     this.val = (val===undefined ? 0 : val)
 5 *     this.next = (next===undefined ? null : next)
 6 * }
 7 */
 8/**
 9 * @param {ListNode} head
10 * @return {ListNode}
11 */
12var reverseList = function (head) {
13  if (head === null || head.next === null) return head
14  const newHead = reverseList(head.next)
15  head.next.next = head
16  head.next = null
17  return newHead
18};