__doPostBack()

__doPostBack()

Define - Use to trigger post back event MANUALLY (and NOT by ASP.NET)  for any ASP.NET control.

Good link to understand it
http://www.codedigest.com/Articles/ASPNET/320_Doing_or_Raising_Postback_using___doPostBack()_function_from_Javascript_in_AspNet.aspx

Simple Jquery Dialog or Input box

Code in *.ascx file
<link href="/sites/9999/_layouts/dialog.css" rel="stylesheet"/>
<link href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.9.2/themes/ui-darkness/jquery-ui.css" rel="stylesheet"/>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js" type="text/javascript"></script>
<script src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.9.2/jquery-ui.min.js" type="text/javascript"></script>
<script src="/sites/9999/_layouts/dialog.js" type="text/javascript" />

<script type="text/javascript"></script>
<table>

<table>
    <tr>
        <td>
            <asp:Button ID="Button1" runat="server" Text="Button" OnClientClick="OpenMyDialog(); return false" />
        </td>
    </tr>
</table>

<div class="container">
    <div class="main">
        <div id="dialog" title="Profile Input">
            <form action="" method="post">
            <label>
                Enter Profile Name:</label>
            <input id="name" name="name" type="text" />
            <br />
            <br />
            <input id="submit" type="submit" value="Ok" class="PopUpOkButton" />
            <input id="close" type="button" value="Close" class="PopUpCloseButton" />
            </form>
        </div>
    </div>
</div>

dialog.js

$(document).ready(function () {

    $(function () {

        $("#dialog").dialog({

            autoOpen: true

        });

    });

    $("#submit").click(function (e) {

        alert($("#name").val());

        return false;

    });

    $("#close").click(function (e) {

        $("#name").val("");

        $("#dialog").dialog("close");

    });

});

function OpenMyDialog() {

    $("#dialog").dialog("open");

}

dialog.css

.PopUpOkButton

{

    border:1px solid #59b4d4;

    background:#0078a3;

    color:#eee;

    padding:3px 0;

    border-radius:5px;

    margin-left:0%;

    cursor:pointer;

    width:80px

}

.PopUpCloseButton

{

    border:1px solid #59b4d4;

    background:#0078a3;

    color:#eee;

    padding:3px 0;

    border-radius:5px;

    margin-left:0%;

    cursor:pointer;

    width:80px

}

Detail reference over here.