<script type="text/javascript">
            // <![CDATA[
            $(document).ready(function(){

                // Set focus to first input
                $('#inputUsername').focus();

                // Custom validator (checks if password == confirm password)
                function confirmPassword(args){
                    if(args.password == args.check)
                        return {valid:true}
                    else
                        return {valid:false, message:'Passwords does not match'}
                }

                // Username is required
                $('#inputPassword, #inputUsername').valid8();

                // Confirm password must match Password
                $('#inputConfirmPassword').valid8({
                    regularExpressions: [
                        {expression: /^.+$/, errormessage: 'Required'}
                    ],
                    jsFunctions:[
                        { 'function': confirmPassword, 'values': function(){
                            return {password: $('#inputPassword').val(), check: $('#inputConfirmPassword').val()}
                        }}
                    ]
                });

                $('#inputUsername').valid8({
                    regularExpressions: [
                        {expression: /^.+$/, errormessage: 'Required'}
                    ],
                    ajaxRequests: [
                        { url: 'class/isUsernameUnique.php', loadingmessage: 'Checking availability...', errormessage:'Username is unavailable'}
                    ]
                });

                $('#inputPolicy').valid8();

                $('#inputEmail').valid8({
                    regularExpressions: [
                        {expression: /^[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?.)+(aero|asia|biz|cat|com|coop|edu|gov|info|int|jobs|mil|mobi|museum|name|net|org|pro|tel|travel.ac|ad|ae|af|ag|ai|al|am|an|ao|aq|ar|as|at|au|aw|ax|az|ba|bb|bd|be|bf|bg|bh|bi|bj|bm|bn|bo|br|bs|bt|bv|bw|by|bz|ca|cc|cd|cf|cg|ch|ci|ck|cl|cm|cn|co|cr|cu|cv|cx|cy|cz|de|dj|dk|dm|do|dz|ec|ee|eg|er|es|et|eu|fi|fj|fk|fm|.fo|fr|ga|gb|gd|ge|gf|gg|gh|gi|gl|gm|gn|gp|gq|gr|gs|gt|gu|gw|gy|hk|hm|hn|hr|ht|hu|id|ie|.il|im|in|io|iq|ir|is|it|je|jm|jo|jp|ke|kg|kh|ki|km|kn|kp|kr|kw|ky|kz|la|lb|lc|li|lk|lr|ls|lt|lu|lv|ly|ma|mc|md|me|mg|mh|mk|ml|mm|mn|mo|mp|mq|mr|ms|mt|mu|mv|mw|mx|my|mz|na|nc|ne|nf|ng|ni|nl|no|np|nr|nu|nz|om|pa|pe|pf|pg|ph|pk|pl|pm|pn|pr|ps|pt|pw|py|qa|re|ro|rs|ru|rw|sa|sb|sc|sd|se|sg|sh|si|sj|sk|sl|sm|sn|so|sr|st|su|sv|sy|sz|tc|td|tf|tg|th|tj|tk|tl|tm|tn|to|tp|tr|tt|tv|tw|tz|ua|ug|uk|us|uy|uz|va|vc|ve|vg|vi|vn|vu|wf|ws|ye|yt|yu|za|zm|zw)b$/, errormessage: 'You sure it is valid? The next step in this registration will be sent to the email you enter here.'}
                    ]
                });

                // Check if all input fields are valid
                $('#buttonSignup').click(function(){
                    alert('Are input fields valid? ' + $('input').isValid());
            });




            });
            // ]]>
        </script>

<?php
    include ("db.php");

    $username = $_POST['value'];

if(!isUsernameUnique($username)){
 $json["valid"] = false;
 $json["message"] = 'username is already in use';
}
else {
 $json["valid"] = true;
}

function isUsernameUnique($username){
 // Database look-up should go here here...
 // But for the sake of this demo a random return will do
     $result = mysql_query("SELECT username FROM users WHERE username ='$username'")
     if ($result > 0);

 return rand(0, 1);
}

print json_encode($json);
    ?>

function isUsernameUnique($username){
 // Database look-up should go here here...
 // But for the sake of this demo a random return will do
     $result = mysql_query("SELECT username FROM users WHERE username ='$username'");
     $num_rows = mysql_num_rows($result);
     if ($num_rows > 0) // userName found
        // return accordingly

}

if ($result) // userName found