This chapter deals with synchronous and asynchronous processing.
10.1. Architecture for client-server data exchange
Dynamically adding elements in a web page traces back to 1996, with the <iframe>. In 1998, Microsoft introduced a more general solution with the ActiveX controls, then in the form of the object
The client-side script program can post a HTTP request and then continue its activity without being blocked. When the mechanism is able to tell that an answer (or an error) is ready, the callback function can be run, on that response, in a similar manner to that of the processing of DOM events.
Beyond the ability to modify only part of the web page, avoiding a complete reload (including many unchanged elements), AJAX also allows access to the data files, under a variety of formats (primarily XML), served ...