document.getElementByID() does not always work on cross browser, and sometime it returns null
In this case, we can use document.getElementsByTagName() to loop through all the “input” and assign values

Example:

var Inputs = document.getElementsByTagName("input");
for (var obj = 0; obj < Inputs.length; obj++){
var Obj = Inputs[obj];
try{
if (Obj.checked){
// some code, do something
switch (Obj.id.toLowerCase()){
case "ordertype":
//some code, do something
break;
}}}
catch (e) {//alert(e); }
}