TYPO3 v8 has reached its end-of-life March 31st, 2020 and is not maintained by the community anymore.
You can order Extended Long Term Support (ELTS) here: TYPO3 ELTS.
AJAX in the TYPO3 Backend¶
In TYPO3 4.2 a new model for writing AJAX code in the TYPO3 Backend was introduced. Although there were some parts in the TYPO3 Backend that used AJAX already, they are now unified into a single interface that handles errors and dispatches the different calls to their final locations. This way it is ensured that e.g. a BE user is logged in and all TYPO3 variables are loaded.
The whole architecture builds on top of successful techniques
developers already know. It's a mixture between the eID concept from
the TYPO3 Frontend, the hooking idea we know from other places in
TYPO3, piped through the single entrypoint file
creates a PHP AJAX object to see if an error occurred or not. If
something went wrong, the X-JSON header is set to false and the
client-side AjaxRequestHandler will know that there is an error.