jquery.post() returns 200 OK from MVC 4 WebAPI, but error-handler is hit

Question

I've got an odd case where my jquery.post returns a code #200 (OK) but the error-handler is hit. This is my MVC WebAPI serverside code (all it does is returning code #200 OK): ``` [HttpPost] public HttpResponseMessage Post(T input) { //_handler.Create(input); return Request.CreateResponse(HttpStatusCode.OK); } ``` and this is my client script ``` ServerAccess.prototype.Save = function (m) { $.post("http://localhost:55482/M/", m) .success( function (o) { alert("success"); }) .error( function (xhr, textStatus, errorThrown) { if (typeof console == 'object' && typeof console.log == 'function') { console.log(xhr); console.log(textStatus); console.log(errorThrown); } } ); }; ``` The console output in Firebug is: POST `http://localhost:55482/M/` 200 OK 894ms Headers Response Headers Content-Length 6 Content-Type application/json; charset=utf-8 Date Sun, 28 Oct 2012 18:55:17 GMT Server Microsoft-HTTPAPI/2.0 Request Headers Accept / Accept-Encoding gzip, deflate Accept-Language nb-no,nb;q=0.9,…

Accepted Answer

Try this instead:

```
ServerAccess.prototype.Save = function (m) {
    $.ajax({
        "type": "POST",
        "url": "http://localhost:55482/M/",
        "data": m,
        "dataType": "json",
        "success": function (data, textStatus, xhr) {
            alert("success");
        },
        "error": function (xhr, textStatus, errorThrown) {
            if (typeof console === 'object' && typeof console.log === 'function') {
                console.log(xhr);
                console.log(textStatus);
                console.log(errorThrown);
            }
        }
    });
};
```

This allows you to set an expected return MIME type of `application/json`.

UPDATE

If you're running your standalone HTML page on `http://localhost:55482`, then it won't be cross-domain. If you're running it on `file:///C:/Users/.../Desktop/test.htm` or somewhere else, then it will be a cross-domain request. `http` versus `https:` also makes the difference.

A `jsonp` request is a `GET` request and cannot be a `POST`. This is because `jsonp` requests are implemented by adding a `<script>` element to the page with the source set to your url, with `data` appended to the querystring (plus a timestamp parameter). Any `POST` requests that expect a `jsonp` return should be automatically converted to `GET` requests.

Finally, since your routine expects data back, you'll need to return some actual data as jQuery will try to parse the JSON that's returned into an object (which it cannot do if no data is returned) and will throw an error if the data cannot be parsed.

Try changing your response message to:

```
String o = "success";
System.Web.Script.Serialization.JavaScriptSerializer ser = new System.Web.Script.Serialization.JavaScriptSerializer();

return Request.CreateResponse(HttpStatusCode.OK, ser.Serialize(o));
```

jquery.post() returns 200 OK from MVC 4 WebAPI, but error-handler is hit

Solution

Problem