xfa.resolveNode question

I have a function that takes 2 arguments, the first is a XFAObject and it doesn't really matter what the second one is. I use the first parameter to set a variable inside a call to xfa.resolveNode(): xfa.resolveNode(x). My variable is a concatination of the parameter and the instanceIndex all in between single quotes of that parameter: x = String.concat("'", param1, "[", param1.instanceIndex, "]'");

When put together it looks like this:

function MyFunction(param1, param2) {

     var j = param1.instanceIndex;

     var x = String.concat("'", param1, "[", j, "]'");

     xfa.resolveNode(x).presence = "visible";

}

Could someone tell me why this isn't working? I checked the values of all my variables and they were all correct, but when it doens't seem to work in the xfa.resolveNode();