Question

Hi I’m looking to check my database when a user signs up to my website to make sure that the username they chose doesn’t already exist and if it does let them know. My code below isn’t working though the returns in the ajax don’t seem to be returned to my form no matter what i do and the form always submits. Why is this happening? Thank you for any help

HTML

<form name="signup" action="Test1.php" onsubmit="return checkUser();" method="get">
Username: <input type="text" name="user" />
<input type="submit" value="Submit" />
</form>

Javascript

<script type="text/javascript" src="jquery-1.7.1.min.js"/></script>
<script type="text/javascript">
    function checkUser(){
        var userV = document.signup.user.value;
        $.ajax({
            url: "Test.php",
            type: "POST",
            data: {user:userV},
            success: function (response) {
                if(response=="0"){
                    //Username already exists notify user
                    return false;
                }else{
                    return true;
                }
            }
        });
    }
</script>

Test.php

<?PHP
    $user = $_POST['user'];
    if($user=="test"){
        die("0");
    }else{
        die("1")
    }
?>

Test1.php

<?PHP
    echo "Form submitted";
?>

Answer 1

You put the return value inside the success callback of your ajax call, whose execution is delayed till server answers.

onsubmit="return checkUser();" expects a true or false value in checkUser() function:

function checkUser(){

   if( stuff )
      return true;
   else
      return false;

}

Anyway this is an overall bad approach because it relies on intrusive javascript. A better solution would be moving all client side logic out of markup:

HTML

<form name="signup" action="Test1.php" method="get">
    <label for="_user">Username:</label><input type="text" name="user" id="_user"/>
   <input type="submit" value="Submit" />
</form>

JS

<script>
// wrapping the code in a $(function(){ ... }); call delays its execution till document is loaded
$(function(){

$('form[name="signup"]').on('submit', function(event){

    // this prevents browser from actually following form url
    event.preventDefault();

    // a reference to the form to get used inside ajax callback
    var form = this;

    $.ajax({
         url: $(form).attr('action'),
         type: "POST",
         data: {user:$(form.user).val()},
         success: function (response) {
             if(response=="0"){

                alert('User exists!');

             }else{

                alert('User does not exist!');

             }
         }
     });

});

});
</script>

Where the alerts would be a proper message to the user, or a more sophisticate validation – this is just for example’s sake.