View source to see the code.
React is spread across a large number of modules. Require1k has no problem loading it, although it does generate a number of 404s. This is because because the parser used in require1k to extract dependencies doesn't understand JavaScript comments. Files like ReactPropTypes.js include require(...) in a comment that does not resolve properly. These 404s slow down loading a bit, but are otherwise harmless
The following container is populated by React: