rollup.config.js

import { resolve } from 'path';
import { outputFileSync } from 'fs-extra';
import { plugin as analyzer } from 'rollup-plugin-analyzer';
import common from 'rollup-plugin-commonjs';
import babel from 'rollup-plugin-babel';
import nodeResolve from 'rollup-plugin-node-resolve';
import { terser } from 'rollup-plugin-terser';

outputFileSync(
  resolve(process.cwd(), 'lib/browser/index.js'),
  `
'use strict';
if (process.env.NODE_ENV === 'production') {
  module.exports = require('./production.min.js');
} else {
  module.exports = require('./development.js');
}
`
);

function getKeys(dependencies = []) {
  return Object.keys(dependencies);
}

const packageJson = require('./package.json'); // eslint-disable-line import/no-dynamic-require
const peerDependencies = getKeys(packageJson.peerDependencies);
const externalModuleNames = [...peerDependencies];

function external(id) {
  return externalModuleNames.some(name => id.startsWith(name));
}

const defaultBabelOptions = {
  configFile: './babel.config.js',
  runtimeHelpers: true
};

const defaultPlugins = [
  nodeResolve({
    extensions: ['.js', '.jsx'],
    modulesOnly: true
  }),
  common(),
  babel(defaultBabelOptions)
];

function writeTo(analysisString) {
  outputFileSync(
    resolve(process.cwd(), 'lib/browser/production.analysis.txt'),
    analysisString
  );
}

export default [
  {
    input: 'src/index.js',
    output: {
      file: 'lib/browser/development.js',
      format: 'esm',
      sourcemap: true
    },
    external,
    plugins: defaultPlugins
  },
  {
    input: 'src/index.js',
    output: {
      file: 'lib/browser/production.min.js',
      format: 'esm',
      sourcemap: true
    },
    external,
    plugins: [...defaultPlugins, terser(), analyzer({ writeTo })]
  }
];