How can I check whether a radio button is selected with JavaScript?

Question

I have two radio buttons within an HTML form. A dialog box appears when one of the fields is null. How can I check whether a radio button is selected?

Answer 1

HTML:

+
-
*
/

JAVAScript:

var options = document.getElementsByName("calculation");

for (var i = 0; i < options.length; i++) {
    if (options[i].checked) {
        // do whatever you want with the checked radio
        var calc = options[i].value;
        }
    }
    if(typeof calc == "undefined"){
        document.getElementById("result").innerHTML = " select the operation you want to perform";
        return false;
}