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

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',

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

When you return a bad request from Controller a global exception is triggered. Probably a error page is displayed in the client, so jquery get 200 response.

Solution 1:

Controller

[HttpPost]
public ActionResult FooAction(string id, string[] orderFields)
{
    bool hasError = true; //TODO: Validation

    if (hasError)
    {
       Response.Clear();
       Response.TrySkipIisCustomErrors = true; //the magic
       Response.StatusCode = (int)HttpStatusCode.InternalServerError;

       return Json(new { success = false, message = "test error", status = 500 });
    }
    else
    {
       return Json(new { success = true, message = "ok", status = 200 });
    }
}

View:

<script type="text/javascript">
    $.ajax({
        type: "POST",
        url: url,
        data: { orderFields: order },
        success: function (response) {
            if (response.success) {
                alert("Ok");
            }
        },
        error: function (xhr, status, error) {
            if (xhr.responseText != "") {
                var err = JSON.parse(xhr.responseText);
                if (err.status == 440) {
                    alert("Session expired");
                }
                else {
                    alert(err.message);
                }
            }
            else {
                alert("Crash");
            }
        }
    });
</script>

Solution 2: (More Elegant)
Create a custom attribute

using System;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Net;
using System.Web.Mvc;

public class ExceptionJsonMvcAttribute : FilterAttribute, IExceptionFilter
{
    public virtual void OnException(ExceptionContext context)
    {
        if (context == null)
        {
            throw new ArgumentNullException("filterContext");
        }

        if (context.Exception == null)
            return;

        int status;
        string message;
        var ex = context.Exception;
        var exceptionType = ex.GetType();
        if (exceptionType == typeof(UnauthorizedAccessException))
        {
            var exAccess = (UnauthorizedAccessException)ex;
            message = exAccess.Message;
            status = (int)HttpStatusCode.Unauthorized;
        }
        else if (exceptionType == typeof(SqlException))
        {
            var exSql = (SqlException)ex;
            message = GetDbMessage(exSql);
            status = (int)HttpStatusCode.BadRequest;
        }
        else if (exceptionType == typeof(KeyNotFoundException))
        {
            var exNotFound = (KeyNotFoundException)ex;
            message = exNotFound.Message;
            status = (int)HttpStatusCode.NotFound;
        }
        else
        {
            message = ex.Message;
            status = (int)HttpStatusCode.InternalServerError;
        }


        string json = ""; // TODO: Json(new { success = false, message = message, status = status });
        context.ExceptionHandled = true;
        context.HttpContext.Response.Clear();
        context.HttpContext.Response.TrySkipIisCustomErrors = true;
        context.HttpContext.Response.StatusCode = status;
        context.HttpContext.Response.ContentType = "application/json";
        context.HttpContext.Response.Write(json);
    }

    private string GetDbMessage(SqlException exSql)
    {
        //TODO: Remove generic from database

        return "DataBase Error see log";
    }
}

pay attention for ApiController use System.Net.Http instead of System.Web.Mvc


Controller:

[ExceptionJsonMvc]
[HttpPost]
public ActionResult FooAction(string id, string[] orderFields)
{
    bool hasError = true; //TODO: Validation

    if (hasError)
    {
       throw new Exception("test error");
    }
    else
    {
       return Json(new { success = true, message = "ok" });
    }
}

.Net Core version, which use the status code to represent server error

C# Code

public string methodName(int param1)
   {
   try{
        Response.StatusCode = 200;
        return "";
    }
   catch {
        Response.StatusCode = 400;
        return "";
        }
   }

ajax call:

 $.ajax({
 type: 'get',
 url: 'your url',
 data: {"param1":value1},
 success: function (data) {
    alert("success");
    },
  error: function () {
    alert("failed");
    }
 });