javascript validation query

$("#submit_js").click(function() {

    $.post(
        "user_submit.php", 
        {score: $('#ques'+qn).find('input[name=vote]:checked').val(), uid:$("#uid").val() }, 
        function(data){

i didnt post the complete fun开发者_StackOverflow社区ction. but that is out of scope. i need to ask how can i validate that the user has chosen a radio button? can someone help me with the syntax?

$('input:radio:checked').length > 0