The most common way to extend the abilities of a web page is through the Common Gateway Interface (CGI). CGI programs run on a web server and deliver information to the user as a new page.

JavaScript might be considered a client-side replacement for CGI. You can now process information on the user's computer instead of a Web server. JavaScript runs on the user's own computer. Sending information across the lines and servers of the Internet slows down its use. Client-side processing helps to reduce these bottlenecks.