rollup.config.js

import svelte from 'rollup-plugin-svelte';
import resolve from 'rollup-plugin-node-resolve';
import commonjs from 'rollup-plugin-commonjs';
import livereload from 'rollup-plugin-livereload';
import { terser } from 'rollup-plugin-terser';

const production = !process.env.ROLLUP_WATCH;

export default {
    input: 'src/main.js',
    output: {
        sourcemap: true,
        format: 'iife',
        name: 'app',
        file: 'public/bundle.js',
    },
    moduleContext: (id) => {
        // In order to match native module behaviour, Rollup sets `this`
        // as `undefined` at the top level of modules. Rollup also outputs
        // a warning if a module tries to access `this` at the top level.
        // The following modules use `this` at the top level and expect it
        // to be the global `window` object, so we tell Rollup to set
        // `this = window` for these modules.
        const thisAsWindowForModules = [
            'node_modules/intl-messageformat/lib/core.js',
            'node_modules/intl-messageformat/lib/compiler.js',
        ];

        if (thisAsWindowForModules.some(id_ => id.trimRight().endsWith(id_))) {
            return 'window';
        }
    },
    plugins: [
        svelte({
            // enable run-time checks when not in production
            dev: !production,
            // we'll extract any component CSS out into
            // a separate file — better for performance
            css: css => {
                css.write('public/bundle.css');
            }
        }),

        // If you have external dependencies installed from
        // npm, you'll most likely need these plugins. In
        // some cases you'll need additional configuration —
        // consult the documentation for details:
        // https://github.com/rollup/rollup-plugin-commonjs
        resolve({
            browser: true,
            dedupe: importee => importee === 'svelte' || importee.startsWith('svelte/')
        }),
        commonjs(),

        // Watch the `public` directory and refresh the
        // browser on changes when not in production
        !production && livereload('public'),

        // If we're building for production (npm run build
        // instead of npm run dev), minify
        production && terser()
    ],
    watch: {
        clearScreen: false
    }
};