rollup.config.js

import babel from 'rollup-plugin-babel'

export default [
  {
    input: 'index.js',
    output: {
      file: 'bundle.js',
      format: 'cjs',
    },
    plugins: [
      babel({
        exclude: 'node_modules/**',
      }),
    ],
  },
  {
    input: 'index.js',
    output: {
      file: 'bundle.es.js',
      format: 'es',
    },
    plugins: [
      babel({
        exclude: 'node_modules/**',
      }),
    ],
  },
]