How can I return a JSON result to a Ajax.BeginForm

I have got this simple form:

@using (Ajax.BeginForm("CreateProductFromAjaxForm","Product" , 
                  null, 
                  new AjaxOptions() {  HttpMethod = "post", OnSuccess = "getresult" },
                  null))
{
    @Html.EditorFor(m => m)
    <hr />
    <div class="form-group">
        <div class="col-md-offset-2 col-md-10">
            <input type="submit" class="btn btn-info" value="Next" />
        </div>
    </div>
}  

And, for testing, a simple controller:

    [HttpPost]
    public JsonResult CreateProductFromAjaxForm(CreateProductModel model)
    {
        if (!ModelState.IsValid)
        {
            return new JsonResult()
            {
                JsonRequestBehavior = JsonRequestBehavior.AllowGet,
                Data = new { result = "error" }
            };
        }

       //add to database

        return new JsonResult()
        {
            JsonRequestBehavior = JsonRequestBehavior.AllowGet,
            Data = new { result = "success"}
        };
    }  

I have added these to the Web.Config:

 <add key="ClientValidationEnabled" value="true" />
 <add key="UnobtrusiveJavaScriptEnabled" value="true" />

and these to my script bundle:

bundles.Add(new ScriptBundle("~/bundles/jquery").Include(
                    "~/Scripts/jquery-{version}.js",
                    "~/Scripts/jquery.validate.js",
                    "~/Scripts/jquery.validate.unobtrusive.js"
                    ));

After clicking the "Submit" button, the resulting page just shows:

{"result":"success"}

I would expect that I could handle the result in the OnSuccess="getresult" handler, but it doesn't seem to work.

Basically I am using the Ajax.BeginForm mainly for the clientside validation.

Can you tell me whats wrong?

UPDATE: I added the HttpMethod = "post" to the AjaxOptions.

UPDATE: The getresult, is defined above the Ajax.BeginForm like this:

<script type="text/javascript">
    var getresult = function (data) {
        alert(data.result);
    };
</script>