.NET MVC JSON Post Call response does not hit complete or success

Question

I am new to .NET MVC so please bear with me.

I wrote a function that gets triggered when there is a blur action on the textarea control:

     function extractURLInfo(url) {
        $.ajax({
            url: "/Popup/Url",
            type: "POST",
            data: { url: url },
            complete: function (data) {
                alert(data);
            },
            success: function (data) {
                alert(data);
            },
            async: true
        })
        .done(function (r) {
            $("#url-extracts").html(r);
        });
    }

    jQuery(document).ready(function ($) {
        $("#input-post-url").blur(function () {
            extractURLInfo(this.value);
        });
    });

This works fine and will hit the controller:

[HttpPost]
        public ActionResult Url(string url)
        {
            UrlCrawler crawler = new UrlCrawler();
            if (crawler.IsValidUrl(url))
            {
                MasterModel model = new MasterModel();
                model.NewPostModel = new NewPostModel();

                return PartialView("~/Views/Shared/Partials/_ModalURLPartial.cshtml", model);
            }
            else
            {
                return Json(new { valid = false, message = "This URL is not valid." }, JsonRequestBehavior.AllowGet);
            }
        }

I get the intended results if the URL is valid; it will return a partialview to the .done() function and I just display it in code. However, if the URL is not valid i want it to hit either complete, success, or done (I have been playing around to see which it will hit but no luck!) and do something with the returned data. I had it at some point trigger either complete or success but the data was 'undefined'. Can someone help me out on this?

Thanks!

Answer 1

In both cases your controller action is returning 200 status code, so it's gonna hit your success callback:

$.ajax({
    url: "/Popup/Url",
    type: "POST",
    data: { url: url },
    success: function (data) {
        if (data.message) {
            // Your controller action return a JSON result with an error message
            // => display that message to the user
            alert(data.message);
        } else {
            // Your controller action returned a text/html partial view
            // => inject this partial to the desired portion of your DOM
            $('#url-extracts').html(data);
        }
    }
});

But of course a much better and semantically correct approach is to set the proper status code when errors occur instead of just returning some 200 status code:

[HttpPost]
public ActionResult Url(string url)
{
    UrlCrawler crawler = new UrlCrawler();
    if (crawler.IsValidUrl(url))
    {
        MasterModel model = new MasterModel();
        model.NewPostModel = new NewPostModel();

        return PartialView("~/Views/Shared/Partials/_ModalURLPartial.cshtml", model);
    }
    else
    {
        Response.StatusCode = 400;
        Response.TrySkipIisCustomErrors = true;
        return Json(new { valid = false, message = "This URL is not valid." }, JsonRequestBehavior.AllowGet);
    }
}

and then in your AJAX call you would handle those cases appropriately:

$.ajax({
    url: "/Popup/Url",
    type: "POST",
    data: { url: url },
    success: function (data) {
        $('#url-extracts').html(data);
    },
    error: function(xhr) {
        if (xhr.status == 400) {
            // The server returned Bad Request status code
            // => we could parse the JSON result
            var data = JSON.parse(xhr.responseText);

            // and display the error message to the user
            alert(data.message);
        }
    }
});

Also don't forget that you have some standard way of returning your error messages you could subscribe to a global .ajaxError() handler in jQuery instead of placing this code in all your AJAX requests.