Merge Nodes in Between Zeros LeetCode solution in JavaScript

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var mergeNodes = function (head) {
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  var res = new ListNode();
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  var ans = res;
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  var current = head.next;
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  var sum = 0;
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  while (current) {
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    if (current.val != 0) {
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      sum = sum + current.val;
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    } else {
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      res.next = new ListNode(sum);
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      sum = 0;
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      res = res.next;
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    }
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    current = current.next;
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  }
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  return ans.next;
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};