Error callback

A callback function invoked if the request fails.

$("form").async({
  error: function(request) {
    // Your code here
  }
});

Trigger a validation

Valide the input content and throw an error if it's not an alphanumeric.

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Success callback demo</title>
  <link rel="stylesheet" href="http://127.0.0.1:4000/assets/css/demo.css">
</head>
<body>
  <form action="/" method="post">
    <input name="xs_username" placeholder="Username">
  </form>

  <script src="https://code.jquery.com/jquery-3.4.0.min.js"></script>
  <script src="https://cdn.jsdelivr.net/npm/form-async/dist/form-async.min.js"></script>
  <script>
     function callback(request) {
       var value = $(this).val(),
           form = $(this).closest("form");

       form.removeClass("error");

       if (/[^a-zA-Z0-9]/.test(value)) {
         form.addClass("error");
         request.abort();
       }
     }

     $("form").async({
        before: callback
     });
  </script>
<body>
</html>

Demo: