rollup.config.js

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

export default [
    // browser-friendly UMD build
    {
        input: 'src/index.js',
        output: {
            name: 'index',
            file: pkg.browser,
            format: 'umd'
        },
        plugins: [
            resolve(), // so Rollup can find `ms`
            commonjs() // so Rollup can convert `ms` to an ES module
        ]
    },

    // 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/index.js',
        external: ['ms'],
        output: [
            { file: pkg.main, format: 'cjs' },
            { file: pkg.module, format: 'es' }
        ]
    },
    {
        input: 'src/extend-expect.js',
        external: ['ms'],
        output: [
            { file: 'extend-expect.js', format: 'cjs' },
        ]
    },

];