(Disclosure: I'm the author of rjsx-mode)

The best setup I've found is to use js2-mode for .js and rjsx-mode for .jsx, which parse the buffer for syntax highlighting, local refactoring (with js2r) and basic linting. For typescript, use typescript-mode. Flow support is quite bad ATM

nvm.el replaces the shell scripts from nvm.

Add a jsconfig.json to your project root and enable tide-mode for completion. This has worked far better than tern-mode, which some people recommend.

For fuller linting than what js2/rjsx offer, use flycheck. Eslint support is built-in, so it should just work, I think.

Finally, for build management, I use prodigy to run webpack, babel, ts, etc. Feel free to ping me if you need more help