rollup.config.js

import svelte from 'rollup-plugin-svelte';
import commonjs from '@rollup/plugin-commonjs';
import resolve from '@rollup/plugin-node-resolve';
import livereload from 'rollup-plugin-livereload';
import { terser } from 'rollup-plugin-terser';
import css from 'rollup-plugin-css-only';
import yaml from '@rollup/plugin-yaml';
import sveltePreprocess from 'svelte-preprocess';

const production = !process.env.ROLLUP_WATCH;

export default {
	input: '_scripts/main.js',
	output: {
		sourcemap: true,
		format: 'iife',
		file: production? 'frontend_build/bundle.js' : '_site/frontend_build/bundle.js'
	},
	plugins: [
		svelte({
			compilerOptions: {
				// enable run-time checks when not in production
				dev: !production
			},
			preprocess: sveltePreprocess({})
		}),
		// we'll extract any component CSS out into
		// a separate file - better for performance
		css({ output: '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/plugins/tree/master/packages/commonjs
		resolve({
			browser: true,
			dedupe: ['svelte']
		}),
		commonjs(),
		yaml(),

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

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