code: function findPrevNode(firstNode, item, comparer) {
      let ret;
      let prevNode = firstNode;
      // while item > prevNode.value
      while (prevNode != undefined && comparer(prevNode.value, item) > 0) {
          ret = prevNode;
          prevNode = prevNode.next;
      }
      return ret;
  }
docs: Seeks the list from the beginning and finds the position to add the new item