Call WebMethod from JS in Visual web Part

Question

I have ASP.NET web app that call some WebMethod from javascipt and fills textboxes. This is not all code, just example codesnippet

function dataApp(text) {

    var loc = window.location.href;
    $.ajax({
        type: "POST",
        url: loc + "/Recount",
        data: JSON.stringify({ 'data': text }),
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        success: OnSuccess,
        error: function (xhr, ajaxOptions, thrownError) {
            $('#mycontrol').val("bla");
            $('#mycontrol2').val("bla");
            // ..
        }
    });
}


// here we get result from server and set some values in web UI
   function OnSuccess(response) {
    var obj = JSON.parse(response.d);

    $('#mycontrol1').val(obj.a);
    $('#mycontrol2').val(obj.b);
}

MyControl.ascx.cs:

[WebMethod]
public static string Recount(string data)
{
// ..
    return JsonString;
}

And it works good while Web Application Project, but now I want to migrate this code to Visual SP web part. And there is a problem connection to web method, in JS console I see(webpart added on default.aspx page):

POST http://server/web/default.aspx/Recount 500 (Internal Server Error)

How can I call my WebMethod from JS in Visual Webpart correctly?

The webpart is fully-featured, not sandboxed.

upd: user asked me an example of ascx file with webmethod, so I put it here:

using System;
using Microsoft.SharePoint;
using Microsoft.SharePoint.WebControls;

namespace CurrencyRate.Layouts.CurrencyRate
{
    using System.Collections.Generic;
    using System.Globalization;
    using System.Net;
    using System.Web;
    using System.Web.Script.Serialization;
    using System.Web.Services;
    using System.Xml;

    public partial class CurrencyRate : LayoutsPageBase
    {
        protected void Page_Load(object sender, EventArgs e)
        {
        }

        /// <summary>
        ///  Update ratings from Yahoo API
        /// </summary>
        [WebMethod]
        public static string RefreshRates(string value)
        {
            try
            {
                // .. 
                return new JavaScriptSerializer().Serialize(
                            new
                                {
                                    error = false,
                                    // some values here
                                });
            }
            catch (Exception ex)
            {
                // ..

                return new JavaScriptSerializer().Serialize(
                        new
                            {
                                error = true,
                                // values
                            });
            }
        }
    }
}

Answer 1

You cant add a WebMethod to a webpart. A webpart is a server control and outputs html to the page. If you want to use webmethods I would create a web service and consume this in the webpart or by other pages / controls.

For these scenarios, we usually have an Application Page which defines all the WebMethods.. And than you can use the application page easily by simply referring to sitecollectionurl + /_layouts/ApplicationPageName.aspx/Recount

Something like:

$.ajax({
     type: "POST",
     url: siteUrl + "/_layouts/SolutionName/WebMethods.aspx/Recount",
     data: "{'data':'" + data + "'}",
     contentType: "application/json; charset=utf-8",
     dataType: "json",
     async: true,
     success: function (data) {
         response(data["d"]);
     },
     error: function (result) {
         //alert("Error");
     }
 });

where siteUrl is site collection Url, you can get it by using _spPageContextInfo.siteServerRelativeUrl or SPClientContext

References:

Embedding a WebMethod in a WebPart

Get a Site Collection and Web Path Using JavaScript in SharePoint 2013