Starting from CubicWeb version 4.0 all code related to generating html views has been moved to the Cube cubicweb_web.
If you want to migrate a project from 3.38 to 4.* while still using all the
html views you need to both install the cubicweb_web cube AND add it to
your dependencies and run
cubicweb_web can be installed from pypi this way:
pip install cubicweb_web
In the long run cubicweb_api will be merged inside of CubicWeb.
For historical reference of what Ajax is and used to be, one can read the wikipedia article about Ajax.
You can, for instance, register some python functions that will become