$.getJSON() not working with ASP.NET MVC2 in jQuery 1.5

Question

I am trying the new jQuery 1.5 and it broke a few things in my application. I make a call to an action that generates the JSON, but something errors out and causes the script to stop. According to Fiddler and Firebug, the action does return JSON data. I didn't provide the JSON data, but the data is valid according to JSONLint.

Please note that this works as expected in jQuery 1.4.4.

The first thing I noticed was the URL: http://localhost:3219/News/GetAllNewsArchives?callback=jQuery15033185029088076134_1296751219270&_=1296751219672

Script:

// Dropdown box for past articles
$("#article-select").ready(function() {
    $.ajaxSetup({ cache: false });
    $.getJSON('/News/GetAllNewsArchives', null, function(json) {
        var items = "<option value=''>(Select)</option>";
        $.each(json, function(i, item) {
            items += "<option value='" + item.Id + "'>" + subject + "</option>";
        });
        $("#article-select").html(items);
    });
});

Action:

    public ActionResult GetAllNewsArchives()
    {
        return Json(newsRepository.GetAllNewsArchives(), JsonRequestBehavior.AllowGet);
    }

Any ideas of what I am doing wrong?

Answer 1

Okay, I switched to a $.ajax call and I had the same error:

// Dropdown box for past articles
$("#article-select").ready(function() {
    $.ajax({
        cache: false,
        type: "POST",
        dataType: "json",
        url: "/News/GetAllNewsArchives",
        success: function(json) {
            var items = "<option value=''>(Select)</option>";
            $.each(json, function(i, item) {
                items += "<option value='" + item.Id + "'>" + subject + "</option>";
            });
            $("#article-select").html(items);
        }
    });

However, I noticed something on the $.ajax() documentation.

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.

I changed my data type from dataType: "json" to dataType: "text json" then it worked.

Now, I just don't understand why the difference. What does json expect that is different?

Answer 2

For some reason, it's interpreting your request as JSONP. In Firebug, inspect the value of $.ajaxSettings and make sure something's not defaulting its dataType to jsonp.

Have you tried using $.ajax() directly, to explicitly set the request's type, dataType, etc?

Answer 3

In jquery 1.5 source code this is the code that detect the content type.

// Remove auto dataType and get content-type in the process
while( dataTypes[ 0 ] === "*" ) {
    dataTypes.shift();
    if ( ct === undefined ) {
        ct = jXHR.getResponseHeader( "content-type" );
    }
}

// Check if we're dealing with a known content-type
if ( ct ) {
    for ( type in contents ) {
        if ( contents[ type ] && contents[ type ].test( ct ) ) {
            dataTypes.unshift( type );
            break;
        }
    }

If you set dataType to "json", the previous code will leave ct as undefined. This is why it does not work as expected. It is a problem in jQuery 1.5, as it breaks compatibility with previous versions of jQuery.

So you should set dataType to "text json" or remove dataType so the default value is used.

Defaults:

    converters: {

        // Convert anything to text
        "* text": window.String,

        // Text to html (true = no transformation)
        "text html": true,

        // Evaluate text as a json expression
        "text json": jQuery.parseJSON,

        // Parse text as xml
        "text xml": jQuery.parseXML
    }

Answer 4

What's the content-type that's in the response? Not what you're asking for, or specify on the dataType parm, but what's the server sending back as the content-type of the response (from fiddler)