How to refer the values in dropdown from WebService response?

In my Adobe Interactive form,

I have Course Type ID and Course Name fields.

Course name is a dropdown that gets filled in the Form Ready event and the "Specify Item Values" is attached to

!connectionData.FetchCourseType.Body.ZFETCHCOURSETYPEResponse.ZCOURSETYPES.item[*]

Now in the TAB event of Course Type ID, I am fetching the Course name and adding to the above dropdown.

But it is adding duplciates.

So to delete the duplicates, I need to read the WebService response in the TAB even of Course ID.

I tried something like

particulars = xfa.datasets.resolveNode("this.parent.COURSENAME");

(var i = 1; i < particulars.nodes.length; i++)

{
p = particulars.nodes.item(i);

But here p.vlaue is blank
break;
}

Can you please provide suitable syntax to achieve this?