AJAX is the good way to avoid postback while executing server side code behind.
use AJAXUpdate panel control exist in AJAX control toolkit, By using UpdatePanel controls, you can refresh selected parts of the page instead of refreshing the whole page with a postback. This is referred to as performing a partial-page update, The UpdatePanel control is a server control that helps you develop Web pages with complex client behavior that makes a Web page appear more interactive to the end user
see below links
Editor, DotNetSpider MVM
Microsoft MVP 2014 [ASP.NET/IIS]