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

this is a utility function I've created to solve this problem

    //define radio buttons, each with a common 'name' and distinct 'id'. 
    //       eg- 
    //           
    //param-sGroupName: 'name' of the group. eg- "storageGroup"
    //return: 'id' of the checked radioButton. eg- "localStorage"
    //return: can be 'undefined'- be sure to check for that
    function checkedRadioBtn(sGroupName)
    {   
        var group = document.getElementsByName(sGroupName);

        for ( var i = 0; i < group.length; i++) {
            if (group.item(i).checked) {
                return group.item(i).id;
            } else if (group[0].type !== 'radio') {
                //if you find any in the group not a radio button return null
                return null;
            }
        }
    }