rollup.config.mjs

import resolve from '@rollup/plugin-node-resolve';
import commonjs from '@rollup/plugin-commonjs';
import alias from '@rollup/plugin-alias';
import json from '@rollup/plugin-json';

const inputOptions = (isWeb) => ({
	input: 'src/index.js',
	plugins: [
		resolve(),
		commonjs(),
		json(),
		alias({
			entries: [
				isWeb && ({ find: './fetch.*.js', replacement: './fetch.browser.js' }),
				!isWeb && ({ find: './fetch.*.js', replacement: './fetch.node.js' }),
			].filter(x => x)
		})
	],
	external: [
		// dependencies that should not be bundled into the file
		'fetch-cookie',
		'msgpack-lite',
		'qrcode',
		'rfc4648',
		'xregexp',
	],
});

export default [
	{
		output: {
			file: 'dist/index.node.mjs',
			format: 'esm',
		},
		...inputOptions(false),
	},
	{
		output: {
			file: 'dist/index.node.cjs',
			format: 'cjs',
		},
		...inputOptions(false),
	},
	{
		output: {
			file: 'dist/index.browser.js',
			format: 'esm',
		},
		...inputOptions(true),
	}
];