Today, ASP.NET offers new models for this aspect of development giving developers a number of options.
The common functionality of button rollover consists of a mouse hover over a button causing the button to change color or shade. This simple function proves important in rich web applications or systems with substantial fields and buttons. The HTML DOM event onmouseover mixed into standard control code provides the functionality, and virtually any other event can be used in a similar way.
Beyond useful snippets in controls, larger functions can be employed. There are 2 ways to achieve this: the RegisterStartupScript method and the RegisterClientScriptBlock method. The RegisterStartupScript method renders script after all elements load, which prevents the script from attempting to manipulate missing elements (i.e., those which have not loaded yet).