rollup.config.js

import commonjs from '@rollup/plugin-commonjs';
import json from '@rollup/plugin-json';
import resolve from '@rollup/plugin-node-resolve';
import replace from '@rollup/plugin-replace';
import babel from 'rollup-plugin-babel';
import svelte from 'rollup-plugin-svelte';
import { terser } from 'rollup-plugin-terser';
import config from 'sapper/config/rollup.js';
import sveltePreprocess from 'svelte-preprocess';
import pkg from './package.json';

const mode = process.env.NODE_ENV;
const dev = mode === 'development';
const legacy = !!process.env.SAPPER_LEGACY_BUILD;

const onwarn = (warning, onwarn) => (warning.code === 'CIRCULAR_DEPENDENCY' && /[/\\]@sapper[/\\]/.test(warning.message)) || onwarn(warning);

const preprocess = sveltePreprocess({
	scss:    {
		includePaths: ['src'],
	},
	postcss: {
		plugins: [require('autoprefixer')],
	},
});

export default {
	client: {
		input:   config.client.input(),
		output:  config.client.output(),
		plugins: [
			replace({
				'process.browser':      true,
				'process.env.NODE_ENV': JSON.stringify(mode),
			}),
			svelte({
				dev,
				hydratable: true,
				emitCss:    true,
				preprocess,
			}),
			resolve({
				browser: true,
				dedupe:  ['svelte'],
			}),
			commonjs(),
			json(),

			legacy && babel({
				extensions:     ['.js', '.mjs', '.html', '.svelte'],
				runtimeHelpers: true,
				exclude:        ['node_modules/@babel/**'],
				presets:        [
					[
						'@babel/preset-env', {
						targets: '> 0.25%, not dead',
					},
					],
				],
				plugins:        [
					'@babel/plugin-syntax-dynamic-import',
					[
						'@babel/plugin-transform-runtime', {
						useESModules: true,
					},
					],
				],
			}),

			!dev && terser({
				module: true,
			}),
		],

		onwarn,
	},

	server: {
		input:    config.server.input(),
		output:   config.server.output(),
		plugins:  [
			replace({
				'process.browser':      false,
				'process.env.NODE_ENV': JSON.stringify(mode),
			}),
			svelte({
				generate: 'ssr',
				dev,
				preprocess,
			}),
			resolve({
				dedupe: ['svelte'],
			}),
			commonjs(),
			json(),
		],
		external: Object.keys(pkg.dependencies).concat(
			require('module').builtinModules || Object.keys(process.binding('natives')),
		),

		onwarn,
	},

	serviceworker: {
		input:   config.serviceworker.input(),
		output:  config.serviceworker.output(),
		plugins: [
			resolve(),
			replace({
				'process.browser':      true,
				'process.env.NODE_ENV': JSON.stringify(mode),
			}),
			commonjs(),
			json(),
			!dev && terser(),
		],

		onwarn,
	},
};