Minimal Babel setup for use with React "hello world". External dependencies purposefully not handled—see https://mixmax.com/blog/rollup-externals for solutions.

main.js

import React from 'react';
import ReactDOM from 'react-dom';

ReactDOM.render(
  <h1>Hello, world!</h1>,
  document.getElementById('root')
);

package.json

{
  "name": "test",
  "version": "1.0.0",
  "description": "",
  "main": "main.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "build": "rollup -c"
  },
  "author": "",
  "license": "MIT",
  "devDependencies": {
    "babel-core": "^6.26.0",
    "babel-preset-react": "^6.24.1",
    "rollup": "^0.52.0",
    "rollup-plugin-babel": "^3.0.2"
  }
}

rollup.config.js

import babel from 'rollup-plugin-babel';

export default {
  input: 'main.js',
  output: {
    file: 'bundle.js',
    format: 'iife'
  },
  plugins: [
    babel({
      presets: ['react']
    })
  ]
};