Client (Single Page) Applications
AJAX allows you to load data without refreshing the page. It is most used in frameworks such as Angular and Ember. Once built, such applications are sent to the browser and any subsequent rendering is done on the client side (in the browser).
This frontend communicates with the backend via HTTP using JSON or XML responses.
Some libraries and frameworks, such as React and Ember, allow you to run applications on both the server and the client.
In this case, the application uses both AJAX and server-rendered HTML to communicate the front-end with the back-end.