leetcode:
https://leetcode.com/problems/reverse-linked-list/
/**
* Definition for singly-linked list.
* function ListNode(val) {
* this.val = val;
* this.next = null;
* }
*/
/**
* @param {ListNode} head
* @return {ListNode}
*/
var reverseList = function(head) {
var prev = null, cur = head, next;
while (cur !== null) {
next = cur.next;
head = cur;
cur.next = prev;
prev = cur;
cur = next;
}
return head;
};