Do you Python or JavaScript for a newbie on the current requirement who has prior knowledge on c++.

I don't know python, but I've seen some of its syntax and I think JavaScript is closer to C++ even know it's vastly different.

JavaScript

Unless we're talking of an old klingon sub-dialect, syntax should play no role in choosing/avoiding a language. It takes no time to learn a new syntax.

All in all, I believe python allows to reuse more concepts learnt on C++ rather than JS.

That said, as a language and its relative stack, I'd always go for JS in the areas where these two langs are competing, but that's another story and it's not the point here.