rollup.build.js

const rollup = require('rollup');
const babel = require('rollup-plugin-babel');
const resolve = require('rollup-plugin-node-resolve');
const commonjs = require('rollup-plugin-commonjs');

const plugins = [
 resolve({}),
 commonjs(),
 babel({
 babelrc: false,
 presets: [
 [
 'env',
 {
 targets: {
 node: 'current',
 },
 modules: false,
 loose: true,
 },
 ],
 ],
 }),
];

async function build() {
 let inputOptions = {
 input: 'src/react.index.js',
 plugins: plugins,
 };

 let outputOptions = {
 format: 'es',
 file: 'priv/elixir_script/react.js',
 sourcemap: 'inline',
 };

 let bundle = await rollup.rollup(inputOptions);
 await bundle.write(outputOptions);

 inputOptions = {
 input: 'src/react_dom.index.js',
 plugins: plugins,
 };

 outputOptions = {
 format: 'es',
 file: 'priv/elixir_script/react_dom.js',
 sourcemap: 'inline',
 };

 bundle = await rollup.rollup(inputOptions);
 await bundle.write(outputOptions);
}

build();