jQuery may be a powerful JavaScript library that permits you to call ASP.NET page method directly without any postback. you can call page method while not involving ScriptManager at all.

Creating page method:
First we've got to make page method, it ought to be declared as static with the [WebMethod] attribute.    [WebMethod]
    public static string GetDate()
    {
        return DateTime.Now.ToString();
    }

jQuery.ajax method:
           $.ajax({
                    type: "POST",
                    contentType: "application/json; charset=utf-8",
                    url: "Default.aspx/MethodName",
                    data: "{}",
                    dataType: "json",
                    success: function (msg) {
                       //do something
                    }
                });

Type: the type of request the type ("POST" or "GET")
URL: A string containing the URL to that the request is sent.
ContentType: By default we've got to use "application/x-www-form-urlencoded; charset=UTF-8", when we sending information to server we've got to use this content type, that is okay for many cases.
Data: data send to be server, if data isn't a string it’ll be converted to query string.
DataType: the type of data that you are expecting back from the server.

Source code:
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>jQuery AJAX call</title>
    <script type="text/javascript" src="http://code.jquery.com/jquery-1.7.1.js"></script>
    <script type="text/javascript">
        $(document).ready(function () {
            // Add the page method call as an onclick handler for the div.
            $('#btnGetTime').click(function () {
                $.ajax({
                    type: "POST",
                    contentType: "application/json; charset=utf-8",
                    url: "Default.aspx/GetDate",
                    data: "{}",
                    dataType: "json",
                    success: function (msg) {
                        alert('Current Time is ' + msg.d);
                    }
                });
            });
        });
    </script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <input type="button" id="btnGetTime" value="Get Time" />
    </div>
    </form>
</body>
</html>

C# code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.Services;
public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
    }
    [WebMethod]
    public static string GetDate()
    {
        return DateTime.Now.ToString();
    }
}

Output:

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