build.js

console.time('build')

const fs = require('fs-extra')
    , rollup = require('rollup')
    , commonjs = require('rollup-plugin-commonjs')
    , json = require('rollup-plugin-json')
    , nodeResolve = require('rollup-plugin-node-resolve')
    , buble = require('rollup-plugin-buble')
    , uglify = require('rollup-plugin-uglify')
    , stylus = require('stylus')
    , nib = require('nib')

fs.copySync('./static', './public', { clobber: true })
fs.ensureDir('./public/css')
fs.ensureDir('./public/js')

module.exports = rollup.rollup({
  entry: 'src/app.js',
  plugins: [
    json(),
    commonjs(),
    nodeResolve(),
    buble(),
    uglify({ mangle: true, compress: true })
  ]
})
.then(bundle => {
  bundle.write({
    format: 'iife',
    dest: 'public/js/app.js',
    sourceMap: true
  })

}).catch(e => {
  console.error(e)
  process.exit(1)
})

const style = stylus(fs.readFileSync('src/css/style.styl', 'utf8'))
.set('filename', 'src/css/style.styl')
.set('compress', true)
.set('sourcemap', {})
.use(nib())
.import('nib')

style.render((err, css) => {
  if (err)
    throw err

  fs.writeFileSync('public/css/style.css', css.replace('URL=src/css/', 'URL='), 'utf8')
  fs.writeFileSync('public/css/style.css.map', JSON.stringify(style.sourcemap), 'utf8')
})

process.on('exit', () => console.timeEnd('build'))