rollup.config.js

import babel from 'rollup-plugin-babel'
import bundleSize from 'rollup-plugin-bundle-size'
import commonjs from 'rollup-plugin-commonjs'
import nodeResolve from 'rollup-plugin-node-resolve'
import pkg from './package.json'

const input = './src/index.js'

const external = ['react']

export default [
  {
    input,
    output: {
      file: pkg.main,
      format: 'cjs'
    },
    external,
    plugins: [
      babel({
        runtimeHelpers: true,
        plugins: ['@babel/transform-runtime']
      }),
      nodeResolve(),
      commonjs(),
      bundleSize()
    ]
  },

  {
    input,
    output: {
      file: pkg.module,
      format: 'esm'
    },
    external,
    plugins: [
      babel({
        runtimeHelpers: true,
        plugins: [['@babel/transform-runtime', { useESModules: true }]]
      }),
      nodeResolve(),
      commonjs(),
      bundleSize()
    ]
  }
]