Javascript is not working with AJAX

If you are using AJAX, and control (inside an UpdatePanel) causes a postback that would normally run Javascript, and you find the Javascript is not running, add a Postback Trigger to the UpdatePanel using the ID of the control that causes the postback.

And this would solve the issue.

Source: https://www.nilebits.com/blog/2008/04/javascript-not-working-with-updatepanel/