Enabling/disabling a button with jquery.validationEngine

Question

I'm using this jQuery form validator but I cannot understand how to make one simple thing here: if form is not valid disable the submit button, otherwise enable submit button.

A little bit of code:

<script type="text/javascript">
$(document).ready(function() {
    $("#registration_form").validationEngine({
        //
    });
});
</script>

<?php
echo "<form id=\"registration_form\">";

echo "<label for=\"name\">Name</label>";
echo "<input class=\"validate[required,custom[onlyLetter],length[3,100]]\" id=\"name\"><br />";

echo "<button type=\"submit\" id=\"submit_button\">GO</button>";
echo "</form>";
?>

Answer 1

This is the script

 <script type="text/javascript">
    $(document).ready(function() {
        $("#registration_form").validationEngine(
    {
        inlineValidation: true
        });
    $('.change').change(function() {
        validate();
    });
    validate();
     });
     function validate(){
     var res = $.validationEngine.loadValidation("#name");
     if (!res)
         $("#submit_button").attr('disabled',''); 
     else
         $("#submit_button").attr("disabled","disabled"); 
 }
 </script>

in the body

<input class="validate[required,custom[onlyLetter],length[3,100]] change" 
   id="name" value=""><br />   

try and feedback me