Modern web applications are moving toward JavaScript-based rich clients that communicate with RESTful APIs and services. The browser acts as the rich client using HTML5, CSS3, and JavaScript, while the server side provides cloud-hosted RESTful services using technologies like Spring and NoSQL databases for scalability. This shifts complexity from server-side rendering to the client while taking advantage of the cloud. Key challenges include implementing modularity in JavaScript and supporting offline use, cloud deployment, API design best practices, and testing.