How can I implement AJAX forms with async validation in ASP.NET MVC?

How can I implement AJAX forms with async validation in ASP.NET MVC?

You can use jQuery AJAX to submit your form asynchronously. For async validation, create a controller action that returns validation results.

Can you show me a code example for the controller action?

Sure! Here's a simple example:

public JsonResult ValidateUsername(string username) {
    var isValid = !db.Users.Any(u => u.Username == username);
    return Json(isValid, JsonRequestBehavior.AllowGet);
}

What about the client-side code to handle the AJAX request?

You can use jQuery like this:

$('#myForm').submit(function(e) {
    e.preventDefault();
    $.ajax({
        url: '/Controller/ValidateUsername',
        type: 'POST',
        data: { username: $('#username').val() },
        success: function(response) {
            if (response) {
                // proceed with form submission
            } else {
                // show validation error
            }
        }
    });
});