asp.net ajaxtoolkit modalpopupextender open server side and cleint Side

Following code will help for how to open ajaxtoolkit modalpopupextender

how it can open via server side code (c#) or cleient Side code

javascript
==========
var launch = false;
function launchModal() {
launch = true;
}

function pageLoad() {
if (launch) {
$find("modalpopupextender client id need to pass here").show();
}
}

Client Side
============

OnClientClick="launchModal()"

serverside:=
============

Following code need to write in any button control click event

ClientScript.RegisterStartupScript(this.GetType(), "key", "launchModal();", true);