This approach is deprecated in favor of using cwclientlibjs. If your use react for your UI, try the react components from the cwelements library. The documentation is kept here as reference.

For historical reference of what Ajax is and used to be, one can read the wikipedia article about Ajax.

CubicWeb provides a few helpers to facilitate javascript <-> python communications.

You can, for instance, register some python functions that will become callable from javascript through ajax calls. All the ajax URLs are handled by the cubicweb.web.views.ajaxcontroller.AjaxController controller.