js 单链表的反转

var reverseList = function (head) {
  // 闭包
  if (head === undefined || head === null) return null;
  var originalHead = head;
  var reverseHead;

  var reverse = function (head) {
    if (head.next === null) {
      reverseHead = head;
      return head;
    } else {
      var node = reverse(head.next);
      node.next = head;
      if (originalHead === head) {
        head.next = null;
        return reverseHead;
      } else {
        return head;
      }
    }
  }

  return reverse(head)
}