At the end of the 90s, the Web development team argued that the computing power of the server is clearly superior to the clients and for this reason dynamically generated content should be generated on web servers or application servers and the client gets a static HTML page in the browser is shown.
The client with the browser was purely limited to the presentation of content, while the application and data retention layer was located on the server.
In 2005, Ajax came up with a technology that took a completely new approach. On the client, the "Ajax Engine" provides an active component that processes user actions and, if necessary, sends requests to the server and evaluates responses. It gives the user the impression that basically the entire application runs on the client.
Today you can see many more frameworks, such as AngularJS, React or Vue.js using this approach. In addition, new protocols, such as e.g. WebSockets, which insist that information be processed and processed on the client.
This turnaround also affects the performance of a web application. While in the past the response times of the server could tell the speed of the application, today the performance depends essentially on the computing speed of the client. Thus, the test must be much more thoughtful in terms of test environments, since the web application can be used by a large number of different devices.