如何使用Javascript构建增强功能？

I'm building an application using ASP.Net MVC, and I want/need it to work with and without javascript enabled. The first stumbling point for me is this: When the user clicks on the register link, if they don't have javascript enabled they should be sent to a registration page that has master page stuff around it... but if they do have javascript enabled then I want the registration form (the same thing from the registration page to come up in a div above the page and fade out the background...I'm building an application using ASP.Net MVC,