When handling an ASP.NET server-side button’s Click event, you may want to do some client-side checking and possibly prevent the posting of a page back to the server.

However, because the Click event is written on the server-side, the page is posted back to the server, which fires the button’s Click event. To prevent this, insert a little JavaScript code which adds a client-side onclick event for the button:

btnClickMe.Attributes.Add("onclick", "return ClickMe();");

The function ClickMe() should be present on the client-side:

<script language="javascript" type="text/javascript">    function ClickMe()    {        //Your code here...        //If particular condition is false then prevent postback        if(condition is false)        {            return false;        }    }

Do your validations in this function and, if your condition is false, it will prevent the page postback with this single line:

  'return false;'

Returning a false value prevents further execution and, thus, the page from posting back to the server. If your conditions are right, the page will be posted back to the server and fire the button’s server-side Click event.