javascript validation for radio button in php.

<input type='radio' class='w1' name='w1' value='1'>1<br>
<input type='radio' class='w1' name='w1' value='2'>2<br>
<input type='radio' class='w1' name='w1' value='3'>3<br>

<script>
if ( $(':radio[class=w1]').attr('checked') != 'checked' ) {
    alert('Radio not checked');
}
</script>

Enjoy!