react package contains only the functionality necessary to define React components. It is typically used together with a React renderer like
react-dom for the web, or
react-native for the native environments.
Note: by default, React will be in development mode. The development version includes extra warnings about common mistakes, whereas the production version includes extra performance optimizations and strips all error messages. Don’t forget to use the production build when deploying your application.
var React = require('react');