How to send html form values and file with javascript to webapi

Question

I need your helps. I'm making cordova project with VS 2015 Community. My problem:

 <form id="formplace" enctype="multipart/form-data" method="post" action="http://localhost:57754/api/app/PostFile">
    <input type="text" id="title" name="title" >
    <input id="sesid" type="hidden" name="ID" />
    <textarea type="text" id="content" name="content" ></textarea>
    <input type="file" id="fileUpload" name="fileUpload" accept="image/*" />
    <input type="submit" value="Send" />

I can send form values to webapi use form's action. Image upload is Ok. But then I can't use return value from server. I want to send this value use javascript. I tried formdata but I couldn't.

My C# codes :

public async Task<HttpResponseMessage> PostFile()
            {
               if (!Request.Content.IsMimeMultipartContent("form-data"))
                {
                    throw new HttpResponseException(HttpStatusCode.UnsupportedMediaType);
                }

                try
                {
                    var uploadFolder = HostingEnvironment.MapPath("/Content/Upload/");

                    Directory.CreateDirectory(uploadFolder);
                    var streamProvider = new MyFormDataStreamProvider(uploadFolder);

                    await Request.Content.ReadAsMultipartAsync(streamProvider);


                    foreach (var key in streamProvider.FormData.AllKeys)
                    {
                        foreach (var val in streamProvider.FormData.GetValues(key))
                        {
                            if (key == "title")
                            {
                                title = val;
                            }
                            else if (key == "content")
                            {
                                content = val;
                            }
                            else if (key == "ID")
                            {
                                ide = val;
                            }
                        }
                    }
                    News n = new News() { };
                    n.ID = ide;
                    n.Photo = "Content/Upload/"+ dateklasor +"/"+ large1;
                    n.PhotoSlider = "Content/Upload/" + dateklasor + "/" + medium1;
                    n.PhotoThumb = "Content/Upload/" + dateklasor + "/" + thumbnail1;
                    n.Title = title;
                    n.Content = content;

                    NewPlace(n);

                    var response = new HttpResponseMessage();
                    response.Content = new StringContent("Success");

                    return response;

                }
                catch (System.Exception e)
                {
                    var response = new HttpResponseMessage();
                    response.Content = new StringContent("Trouble");
                    return response;
                }
            }

I'm sending with ajax but server side throw excepiton Message = "Unexpected end of MIME multipart stream. MIME multipart message is not complete." – What should I do? Thanks for helps.