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

Let's pretend you have HTML like this

<input type="radio" name="gender" id="gender_Male" value="Male" /><input type="radio" name="gender" id="gender_Female" value="Female" />

For client-side validation, here's some Javascript to check which one is selected:

if(document.getElementById('gender_Male').checked) {  //Male radio button is checked}else if(document.getElementById('gender_Female').checked) {  //Female radio button is checked}

The above could be made more efficient depending on the exact nature of your markup but that should be enough to get you started.

If you're just looking to see if any radio button is selected anywhere on the page, PrototypeJS makes it very easy.

Here's a function that will return true if at least one radio button is selected somewhere on the page. Again, this might need to be tweaked depending on your specific HTML.

function atLeastOneRadio() {    return ($('input[type=radio]:checked').size() > 0);}

For server-side validation (remember, you can't depend entirely on Javascript for validation!), it would depend on your language of choice, but you'd but checking the gender value of the request string.

With jQuery, it'd be something like

if ($('input[name=gender]:checked').length > 0) {    // do something here}

Let me break that down into pieces to cover it more clearly.jQuery processes things from left to right.

input[name=gender]:checked

1. input limits it to input tags.
2. [name=gender] limits it to tags with the name gender within the previous group.
3. :checked limits it to checkboxes/radio buttons that are selected within the previous group.

If you want to avoid this altogether, mark one of the radio buttons as checked (checked="checked") in the HTML code, which would guarantee that one radio button is always selected.

A vanilla JavaScript way

var radios = document.getElementsByTagName('input');var value;for (var i = 0; i < radios.length; i++) {    if (radios[i].type === 'radio' && radios[i].checked) {        // get value, set checked flag or do whatever you need to        value = radios[i].value;           }}