How to call .ashx file through jquery

your aspx page.
add the latest jquery into the head section

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js" type="text/javascript"></script>

<script>
//document ready
$(function(){
$.ajax({
            type: "POST",
            url: "handler.ashx",
            data: { firstName: 'Rahul', lastName: 'Kumar' },
            // DO NOT SET CONTENT TYPE to json
            // contentType: "application/json; charset=utf-8",
            // DataType needs to stay, otherwise the response object
            // will be treated as a single string
            dataType: "json",
            success: function (response) {
                alert(response.d);
            }
        });
});
</script>

your handler.ashx file

    using System;
    using System.Web;
    using Newtonsoft.Json;

    public class Handler : IHttpHandler
    {
        public void ProcessRequest(HttpContext context)
        {
            context.Response.ContentType = "text/plain";

            string myName = context.Request.Form["firstName"];

            // simulate Microsoft XSS protection
            var wrapper = new { d = myName };
            // in order to use JsonConvert you have to download the
            // Newtonsoft.Json dll from here  http://json.codeplex.com/
            context.Response.Write(JsonConvert.SerializeObject(wrapper));
        }

        public bool IsReusable
        {
           get
           {
                return false;
           }
        }
    }