I have a JavaScript function as follows:

function popup(username) {

var req = createAjaxObject();

var message = prompt(Message:,);

if(message != ){

    req.onreadystatechange = function() {

        if (req.readyState == 4) {

            alert(req.responseText);

        }

    }

    req.open('POST','getmessage.php',true);

    req.setRequestHeader(Content-type,application/x-www-form-urlencoded);

    req.send(username= + username +&message=+message);

} else {

    alert(Please enter a message);

}

}

When the Cancel button is hit, the form is still processed through getmessage.php. Any way to have the Cancel button do nothing?

EDIT:

Here is the way this function is called:

                <?php

        mysqlLogin();

        $username = $_COOKIE['sqlusername'];

        $sql = mysql_query(SELECT username FROM `users` WHERE username!='$username');

        if(mysql_num_rows($sql) != 0) {

            echo <table class='usertable' align='center'>;

            while($row = mysql_fetch_array($sql)){

                $username = $row['username'];

                echo <tr><td><center> . $row['username'] . </center></td><td>&nbsp;&nbsp;<a href='#' onClick=popup('$username');>Send Message</a></td></tr>;

            }

            echo </table>;

        } else {

            echo <center>No users found!</center>;

        }



    ?>

The PHP script its linked to:

<?php

$id = rand(1,1500);

$poster = $_POST['username'];

$message = $_POST['message'];

$to = $_COOKIE['sqlusername'];



require('functions.php');

mysqlLogin();



$sql = mysql_query(INSERT INTO `messages` VALUES ('$id','$message','$to','$poster',''));

if($sql){

    echo Message sent!;

} else {

    echo Woops! Something went wrong.;

}

?>