Hi
This is an excellent article to be use as a reference.
We can definitely use Jquery / AngularJS anything at front-end. The basic concept is to communicate with DB vis REST API or Directly calling the functions.
I don't see any harm in using them. Only thing one should keep in his/her mind is, if CRUD is done via REST APIs, then in that case, we should make sure not anyone should able to assess our data from client side. We should have some authentication security checks (May be sending header info with Ajex calls to validate the user etc).
Excellent article by Lokesh and Scott.
Thanks and Regards
Kautuk Sahni