Method that returns type of controls (buttons, radio, textfeild, etc)

Dear all, 

     I'm usinf LiveCycle ES2 and trying to hide all buttons in the PDF forms when a signatures is inputted. To do so, I have to loop through all nodes/fields in the form using the below function, but I could not help finding the method that returns the type pf field/controls so that I only hide buttons not others fields/controls such as textfield, radio, signature etc..Can anyone help me to find the method that return the type of control/field please? The place where I need this method is surrounded by @@@. 

function ProcessAllFields(oNode)
{
if (oNode.className == "exclGroup" || oNode.className == "subform" || oNode.className == "subformSet" || oNode.className == "area")
{
for (var i = 0; i < oNode.nodes.length; i++)
{
var oChildNode = oNode.nodes.item(i);
ProcessAllFields(oChildNode);
}
}
else if (oNode.className == "field" && @@@@ oNode type is "button" @@@)
{
oNode.presence = "hidden";
}
}