[LeetCode][JavaScript]Remove Duplicates from Sorted List

Remove Duplicates from Sorted List

Given a sorted linked list, delete all duplicates such that each element appear only once.

For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3.

https://leetcode.com/problems/remove-duplicates-from-sorted-list/

 1 /**
 2  * Definition for singly-linked list.
 3  * function ListNode(val) {
 4  *     this.val = val;
 5  *     this.next = null;
 6  * }
 7  */
 8 /**
 9  * @param {ListNode} head
10  * @return {ListNode}
11  */
12 var deleteDuplicates = function(head) {
13     var h = new ListNode(-1), tail = h, previous = null;
14     while(head){
15         if(head.val !== previous){
16             tail.next = head;
17             tail = tail.next;
18         }
19         previous = head.val;
20         head = head.next;
21     }
22     tail.next = null;
23     return h.next;
24 };