I need to apply different functions to each dropdown list, but it doesn't work

var btnDrp = grpFldr2.add("dropdownlist", undefined, ["1","2","3"])
btnDrp.selection = 0

var btnApply = grpFldr2.add("button", undefined, "Apply");

if (btnDrp.index == 0) {
    btnApply.onClick = function(){
    alert("Hello")
    }
}