[jquery] Jquery Ajax, return success/error from mvc.net controller

I would like to control when to reply an error message and when a success message but I am always get the error message:

here is what I am trying to do:

 $.ajax({
                type: "POST",
                data: formData,
                url: "/Forms/GetJobData",
                dataType: 'json',
                contentType: false,
                processData: false,

                success: function (response) {                    
                   alert("success!") 
                },
                error: function (response) {
                   alert("error") // I'm always get this.
                }

            });

Controller:

         [HttpPost]
            public ActionResult GetJobData(Jobs jobData)
            {

              var mimeType = jobData.File.ContentType;
              var isFileSupported = AllowedMimeTypes(mimeType);

             if (!isFileSupported){        
                     //  Error
                    Response.StatusCode = (int)HttpStatusCode.BadRequest;
                    return Content("The attached file is not supported", MediaTypeNames.Text.Plain);    
             }
            else
              {
                    //  Success
                    Response.StatusCode = (int)HttpStatusCode.OK;
                    return Content("Message sent!", MediaTypeNames.Text.Plain);     

               }   

            }

When you return value from server to jQuery's Ajax call you can also use the below code to indicate a server error:

return StatusCode(500, "My error");

Or

return StatusCode((int)HttpStatusCode.InternalServerError, "My error");

Or

Response.StatusCode = (int)HttpStatusCode.InternalServerError;
return Json(new { responseText = "my error" });

Codes other than Http Success codes (e.g. 200[OK]) will trigger the function in front of error: in client side (ajax).

you can have ajax call like:

$.ajax({
        type: "POST",
        url: "/General/ContactRequestPartial",
        data: {
            HashId: id
        },
       success: function (response)  {
            console.log("Custom message : " + response.responseText);
        }, //Is Called when Status Code is 200[OK] or other Http success code
        error: function (jqXHR, textStatus, errorThrown)  {
            console.log("Custom error : " + jqXHR.responseText + " Status: " + textStatus + " Http error:" + errorThrown);
        }, //Is Called when Status Code is 500[InternalServerError] or other Http Error code
        })

Additionally you can handle different HTTP errors from jQuery side like:

$.ajax({
        type: "POST",
        url: "/General/ContactRequestPartial",
        data: {
            HashId: id
        },
        statusCode: {
            500: function (jqXHR, textStatus, errorThrown)  {
                console.log("Custom error : " + jqXHR.responseText + " Status: " + textStatus + " Http error:" + errorThrown);
            501: function (jqXHR, textStatus, errorThrown)  {
                console.log("Custom error : " + jqXHR.responseText + " Status: " + textStatus + " Http error:" + errorThrown);
            }
        })

statusCode: is useful when you want to call different functions for different status codes that you return from server.

You can see list of different Http Status codes here:Wikipedia

Additional resources:

1. Returning Server-Side Errors from AJAX Calls
2. Returning a JsonResult within the Error function of JQuery Ajax
3. Handling Ajax errors with jQuery

Use Json class instead of Content as shown following:

    //  When I want to return an error:
    if (!isFileSupported)
    {
        Response.StatusCode = (int) HttpStatusCode.BadRequest;
        return Json("The attached file is not supported", MediaTypeNames.Text.Plain);
    }
    else
    {
        //  When I want to return sucess:
        Response.StatusCode = (int)HttpStatusCode.OK; 
        return Json("Message sent!", MediaTypeNames.Text.Plain);
    }

Also set contentType:

contentType: 'application/json; charset=utf-8',