Frankly, I do not quite understand your question (because the answer seems obvious to me, but that says nothing about others). But from what I understand, you would like to have two major parts of your application:
That is just how many contemporary applications are built.
So the answer to that question
In such a front-end application, is it possible to using client side language
But not only that. There are other usescases:
offline first where you could build your application (at first) only in the browser, having e.g. PouchDB as a "Database"-Layer (in fact it is a facade over some browser technologies using the "couchdb-protocol"), which could easily sync with an "online" couchdb
nobackend which is from a similar ecosystem
Or take a look at draw.io a diagramming app which runs completely in the browser and allows you to use Dropbox as persistence backend.
I want to completely sperate the front-end and back-end, the backend using Java EE stack expose restful web service, the front-end web application interact with back-end using json.
This is quite common.