Should be modern web page based on JS covered sessions by PHP?

I do not know if in modern web pages is still needed to made for example fields values storage also via JS and PHP? I am just interesting about your opinions.

Bcz course which I absolved was based on theory that everything (what can be) must be first done via PHPand then JS. But course is from 2015.

I know that protecion like sanitization of data must be double checked due to safety if someone turn off JS ~(maybe also this can be covered just by htmlcharspecial function).

But it is still needed to count that someone will use browser with JS turned off also for sessions, validation, etc?

Thank you,