rollup.config.js

import resolve from 'rollup-plugin-node-resolve';
import commonjs from 'rollup-plugin-commonjs';
import pkg from './package.json';

const fileName = (format) => pkg.browser.replace('.js', `.${format}.js`)

export default [
    {
        input: 'src/multiRegExp2.js',
        output: [
            {
                name: 'multiRegExp2',
                file: fileName('iife'),
                format: 'iife', // immediately-invoked function expression — suitable for <script> tags
                sourcemap: true
            },
            {
                name: 'multiRegExp2',
                file: fileName('umd'),
                format: 'umd', // universal but bigger module
                sourcemap: true
            }
        ],
        plugins: [
            resolve(), // tells Rollup how to find date-fns in node_modules
            commonjs(), // converts date-fns to ES modules
        ]
    },

    // CommonJS (for Node) and ES module (for bundlers) build.
    // (We could have three entries in the configuration array
    // instead of two, but it's quicker to generate multiple
    // builds from a single configuration where possible, using
    // an array for the `output` option, where we can specify
    // `file` and `format` for each target)
    {
        input: 'src/multiRegExp2.js',
        external: [],
        output: [
            { file: pkg.main, format: 'cjs' },
            { file: pkg.module, format: 'es' }
        ]
    },

    {
        input: 'src/multiRegExp2-test.js',
        external: [],
        output: [
            { file: 'dist/multiRegExp2-test.esm.js', format: 'es' }
        ]
    }
];