I'm have the same issue. the error I get in the browser console is as follows:

I had issues with pulling the existing variable, but did a workaround mapping the variable directly and calling the local storage variable.

Thanks for your help!

Thank you, this worked great!

I tried this without luck. Should the code be triggered on the success of invoking the list service?

Thank you, this worked! I just had to add in -- if(radioButton == null)
otherwise the following code worked great:

var radioButton =$('input[name=mobileradiogroup_5]:checked').val();

if(radioButton -- null){
alert("Please select an option from the list");

return;
};