Is there a Request.IsMvcAjaxRequest() equivalent for jQuery?

public static class HttpRequestBaseExtensions
{
    public static bool IsjQueryAjaxRequest(this HttpRequestBase request)
    {
        if (request == null)
            throw new ArgumentNullException("request");

        return request["__JQUERYASYNCPOST"] == "true";
    }
}

if (Request.IsjQueryAjaxRequest())
    //some code here

$('form input[type=submit]').click(function(evt) {
    //intercept submit button and use AJAX instead
    evt.preventDefault();

    $.ajax(
        {
            type: "POST",
            url: "<%= Url.Action("Create") %>",
            dataType: "json",
            data: { "__JQUERYASYNCPOST": "true" },
            success: function(data) {alert(':)');},
            error: function(res, textStatus, errorThrown) {alert(':(');}
        }
    );
});

if (Request.Headers["X-Requested-With"] == "XMLHttpRequest")
    return Json(...);
else
    return View();

post: function(url, data, callback, type) {
            var postIdentifier = {};
            if (jQuery.isFunction(data)) {
                callback = data;
                data = {};
            }
            else {
                postIdentifier = { __JQUERYASYNCPOST: true };
                jQuery.extend(data, postIdentifier);
            }

            return jQuery.ajax({
                type: "POST",
                url: url,
                data: data,
                success: callback,
                dataType: type
            });
        }