function Node(data) {
  this.data = data;
  this.next = null;
}
function sortedInsert(head, data) {
  let currentNode = head;
  let prevNode = head;
  const target = new Node(data);

  // insert in begining;
  if(!head || target.data < head.data){
    target.next = head;
    return target;
  }

  // insert in middle
  while(currentNode !== null){
    if(currentNode.data > target.data){
      prevNode.next = target;
      target.next = currentNode;
      return head;
    }
    prevNode = currentNode;
    currentNode = currentNode.next;
  }

  // insert in end;
  prevNode.next = target;
  return head;
}