i got the solution reference your javascript file within scriptmanager
add following mandatory lines to execute jquery functions after updatepanel
asynchronous postback
mandatory lines are
Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequest);
bind endrequest function after updatepanel asynchrous postback
function EndRequest() {
init();
}
add functions on document initialization
function init() {
$('#btn1').click(function () {
alert($('#txt').val());
});
}
$(document).ready(init);