rollup.config.js

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

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

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

const extensions = [".svelte", ".svx", ".md"];

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

			legacy && babel({
					extensions: [".js", ".mjs", ".html", ...extensions],
					babelHelpers: 'runtime',
					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
			})
		],

		preserveEntrySignatures: false,
		onwarn
	},

	server: {
		input: config.server.input(),
		output: config.server.output(),
		plugins: [
			replace({
				"process.browser": false,
				"process.env.NODE_ENV": JSON.stringify(mode)
			}),
			svelte({
        extensions,
        hydratable: true,
				preprocess: mdsvex(),
				generate: "ssr",
				dev
			}),
			resolve({
				dedupe: ['svelte']
			}),
			commonjs()
		],
		external: Object.keys(pkg.dependencies).concat(require('module').builtinModules),
		preserveEntrySignatures: 'strict',
		onwarn
	},

	// serviceworker: {
	// 	input: config.serviceworker.input(),
	// 	output: config.serviceworker.output(),
	// 	plugins: [
	// 		resolve(),
	// 		replace({
	// 			"process.browser": true,
	// 			"process.env.NODE_ENV": JSON.stringify(mode)
	// 		}),
	// 		commonjs(),
	// 		!dev && terser()
  //       ],
  //       preserveEntrySignatures: false,
	// 	onwarn
	// }
};