Ajax MVC Partial Returning Correct Response Yet Fires the Error Handler

Question

This has me completely stumped. So odd.

I have this Ajax function defined:

$.ajax({
    type: 'GET',
    dataType: 'text/HTML',
    url: getLicenseeDetailsUrl,
    success: function (response) {
        $('#licenseeDetails').html('');
        $('#licenseeDetails').html(response);
    },
    error: function (xhr) {
        alert('Failed to get licensee details');
    }
});

And I have it calling into my controller which has an action like:

public ActionResult LoadLicenseeDetails(long licenseeId)
{
    var model = new LicenseeDetailsViewModel();

    var licencesee = _licensingRepository.LoadById(licenseeId);
    var licenses = _licensingRepository.LoadLicenses(licenseeId);

    model.Licencee = Mapper.Map<Licensee, LicenceeViewModel>(licencesee);
    model.Licences = Mapper.Map<IEnumerable<License>, IEnumerable<LicenceViewModel>>(licenses);

    return this.PartialView("_LicenseeDetails", model);
}

This all seems to be working as expected without any errors, however it ends up firing the Ajax error function, not the success function.

Looking at the xhr.responseText I can see the correct response information from the action controller!!

All with a status 200 OK as well. What on earth am I doing wrong here?

Answer 1

What on earth am I doing wrong here?

this:

dataType: 'text/HTML'

should become:

dataType: 'html'

Quote from the documentation of the dataType parameter:

dataType (default: Intelligent Guess (xml, json, script, or html))

Type: String

The type of data that you're expecting back from the server. If none is specified, jQuery will try to infer it based on the MIME type of the response (an XML MIME type will yield XML, in 1.4 JSON will yield a JavaScript object, in 1.4 script will execute the script, and anything else will be returned as a string). The available types (and the result passed as the first argument to your success callback) are:

"xml": Returns a XML document that can be processed via jQuery.

"html": Returns HTML as plain text; included script tags are evaluated when inserted in the DOM.

"script": Evaluates the response as JavaScript and returns it as plain text. Disables caching by appending a query string parameter, "_=[TIMESTAMP]", to the URL unless the cache option is set to true. Note: This will turn POSTs into GETs for remote-domain requests.

"json": Evaluates the response as JSON and returns a JavaScript object. The JSON data is parsed in a strict manner; any malformed JSON is rejected and a parse error is thrown. As of jQuery 1.9, an empty response is also rejected; the server should return a response of null or {} instead. (See json.org for more information on proper JSON formatting.)

"jsonp": Loads in a JSON block using JSONP. Adds an extra "?callback=?" to the end of your URL to specify the callback. Disables caching by appending a query string parameter, "_=[TIMESTAMP]", to the URL unless the cache option is set to true.

"text": A plain text string.

multiple, space-separated values: As of jQuery 1.5, jQuery can convert a dataType from what it received in the Content-Type header to what you require. For example, if you want a text response to be treated as XML, use "text xml" for the dataType. You can also make a JSONP request, have it received as text, and interpreted by jQuery as XML: "jsonp text xml." Similarly, a shorthand string such as "jsonp xml" will first attempt to convert from jsonp to xml, and, failing that, convert from jsonp to text, and then from text to xml.

Or even better, simply get rid of this parameter. jQuery is intelligent enough to use the Content-Type response HTTP header set by the server in order to deduce the correct type and process the parameter passed to the success callback.

Look at the Console tab of your javascript debugging toolbar in the browser. It will provide you with more information about the error.