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)

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
      }),
      resolve({
        browser: true,
        dedupe: ['svelte']
      }),
      commonjs(),

      legacy &&
        babel({
          extensions: ['.js', '.mjs', '.html', '.svelte'],
          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({
        generate: 'ssr',
        dev
      }),
      resolve({
        dedupe: ['svelte']
      }),
      commonjs()
    ],
    external: Object.keys(pkg.dependencies).concat(
      require('module').builtinModules
    ),

    preserveEntrySignatures: 'strict',
    onwarn
  }
}