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";

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 dedupe = importee => importee === "svelte" || importee.startsWith("svelte/");

const preprocessOptions = {
	transformers: {
		postcss: {
			plugins: [
				require("postcss-import")(),
				require("postcss-url")(),
			]
		}
	}
};

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,
				preprocess: require("svelte-preprocess")(preprocessOptions)
			}),
			resolve({
				browser: true,
				dedupe
			}),
			commonjs(),

			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
			}),
			resolve({
				dedupe
			}),
			commonjs()
		],
		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(),
			!dev && terser()
		],

		onwarn,
	}
};