javascript selected radio

To get the value of the checked radio button, without jQuery:

var radios = document.getElementsByName("u_type");
for(var i = 0; i < radios.length; i++) {
    if(radios[i].checked) selectedValue = radios[i].value;   
}

(assuming that selectedValue is a variable declared elsewhere)

function addUser() {
    //how to check what is the selected radio input
    alert(getCheckedRadioValue('u_type'));
}

function getCheckedRadioValue(name) {
    var elements = document.getElementsByName(name);

    for (var i=0, len=elements.length; i<len; ++i)
        if (elements[i].checked) return elements[i].value;
}

And element's IDs must be different.