如何在ASP.NET中从客户端调用服务器端函数？

I have a web page having asp.net button control and textbox. I want a confirm message box, when someone changes the content of textbox and click on button. If user click on yes then event of button should fire other wise nothing should happen. All I want is to implement AJAX call back, but it is not working with ASP.NET button control.I have a web page having asp.net button control