Does react-native optimize JavaScript code?

I read a guide on compilers. They have many optimization techniques like removing redundant code or removing unused variables and none used methods.
But script languages like javascript don't have compiler, so take it will not have optimizations.
I read a article about js optimizer like:

- Google Closure Compiler https://github.com/google/closure-compiler- UglifyJS https://github.com/mishoo/UglifyJS

And the real question is Does platforms like react-native, angular, use code optimizer or should I use it myself?