How to prevent second click on radio button if it is already checked so that javascript event can be prevented

Question

How to prevent second click on radio button if it is already checked so that javascript event can be prevented.

As I am doing many things onclick of radio button

<input name="EnumEvent" type="radio" value="Open" onclick="show_event()"/>

javascript

function show_event()
{
    document.getElementById("radio-btns-div1").style.display="block";
    document.getElementById('invited').style.display="none";
    document.getElementById('invited').value = '';
    document.getElementById('invite_1').value='';
}

Answer 1

You could use change event instead of click

<input name="EnumEvent" type="radio" value="Open" onchange="show_event()"/>

DEMO

Answer 2

Add the disabled attribute

function show_event()
{
  document.getElementByName("EnumEvent").setAttribute("disabled", "disabled");
  ...
}

Don't forget to remove the attribute when/if you want the user to be allowed to select another option.