Microcomputers from the 80s booted to a BASIC interpreter REPL. There's no reason why a similar constrained system from the current era couldn't just boot to a JS REPL.
And yes, if you wanted to do anything really significant, you needed to learn assembly. But frankly most did not bother.
And yes, if you wanted to do anything really significant, you needed to learn assembly. But frankly most did not bother.