Some well-known examples of the code on demand paradigm on the web are Java applets, Adobe's ActionScript language for the Flash Player, and JavaScript.
Upon this request, the web page and the program are transported to the user's machine using HTTP.
The server takes care of the back-end stuff (data storage, business rules, etc.)
The last constraint on the client-server communication is that responses from servers must be marked as cacheable or non-cacheable.
An effective cache can reduce the number of client-server interactions, which contributes positively to the performance of the system.