how to add or delete the last repeating row in a dynamic form?

Script Dependencies and "recalculate()"

I follow the example here, and use it to do the dynamic form. The +/- button now work as my Add/Delete row button.

And I find a problem:

the table is created and rows are repeating. I make the row min=1, initial count =4, no max.

But when you click on "Add row"/"Delete row" button, it's adding/deleting the instance of the first row always. I want to modify the last row instead.

my script (most alike the samples):

Add row:

function addRow(addButton){

  /*

    This button will insert one instance of the repeating subform or table row.

    message: The error message displayed.

  */

  var message = "You have reached the maximum number of items allowed.";

  // DO NOT MODIFY THE CODE BEYOND THIS POINT - 8.2.1.3158.1.475346.466429 - Subform_Instance_Controls_IRM.xfo.p2

  var oTargetSubform = addButton.parent.repeatingTable.repeatingRow; // The subform or table row the controls are intended to manipulate.

  var oManager = oTargetSubform.instanceManager; // Get the instance manager.

  var nMaxCount = oManager.occur.max; // Get the maximum number of subform occurrences allowed.

  var nSubCount = oManager.count; // Get the current number of instances.

  // Proceed if the maximum number of subform occurrences has not been reached.

  if ((nMaxCount == "-1") || (nSubCount < nMaxCount)) {

  // Invoke the Instance Manager.

  var oNewInstance = oManager.addInstance(1);

  // Move the new subform below the current one.

  var nIndexFrom = oNewInstance.index;

  var nIndexTo = oTargetSubform.index + 1;

  oManager.moveInstance(nIndexFrom, nIndexTo);

  } else {

  xfa.host.messageBox(message,"Insert Item", 3);

  }

  // END OF DO NOT MODIFY

}

Delete row:

function deleteRow(deleteButton){

  var message = "You have reached the minimum number of items allowed.";

  // Fix for listener problem.

  // Note that we're calling this before we delete the current node, BUT that's okay because the recalculate actually is

  // deferred until after the current script finishes.

  // DO NOT MODIFY THE CODE BEYOND THIS POINT - 8.2.1.3158.1.475346.466429 - Subform_Instance_Controls_IRM.xfo.p4

  var oTargetSubform = deleteButton.parent.repeatingTable.repeatingRow; // The subform or table row the controls are intended to manipulate.

  var oManager = oTargetSubform.instanceManager; // Get the instance manager.

  var nMinCount = oManager.occur.min; // Get the minimum number of subform occurrences allowed.

  var nSubCount = oManager.count; // Get the current number of instances.

  // Proceed if the minimum number of subform occurrences has not been reached.

  if (nSubCount > nMinCount) {

  // Invoke the Instance Manager.

  oManager.removeInstance(oTargetSubform.index);

  } else {

  xfa.host.messageBox(message,"Remove Item", 3);

  }

  // END OF DO NOT MODIFY

}