react_demo$ du -sh node_modules/
    25M     node_modules/
    react_demo$ ls node_modules/|wc -l
    79
    react_demo$ cat $(find node_modules/ -type f ) | wc -l
    287767

I think I installed react, react-dom, browserify (globally), babel. The exact details are not really important, being inexperienced with react I probably installed stuff that is not strictly necessary. However, the ease of pulling in a huge amount of dependent code makes me concerned. For a long lived stable application you will have to maintain those dependencies (at a minimum, have 3rd party maintainers who you can trust to maintain it, not break your app, not inject security issues into your app, etc).