function checkOptionValue(inputObj){
var objLength = inputObj.length;
if(objLength == undefined){
if(inputObj.checked)
return inputObj.value;
else
return "";
}else{
for(var i = 0; i < objLength; i++) {
if(inputObj[i].checked) {
return inputObj[i].value;
}
}
}
return "";
}

Another way to find out if object exists or not

function objExists(objToTest) {
if (null == objToTest) {
return false;
}
if ("undefined" == typeof(objToTest) ) {
return false;
}
return true;
}

function explained

Pass the radio option as form object not the only the name of the radio button.
Example: function like checkOptionValue(document.form1.myoption);

var objLength = inputObj.length; – It gets the length of the radio options.
Example if there are 2 radio input like (male, female) its length will be 2.

if(objLength == undefined){ – Check if there is only one radio option, then length method will return undefined.

if(inputObj.checked) “checked” function returns true or false, true if option is checked/selected.

return inputObj.value; return the value of checked option.

Else return “”; if its not check return empty string.

Else do a loop based on the length of the radio object

Keep checking if any option found checked return its value.

Working Example

NEXT: Setting the radio option value with javascript.