Taks sample

task.js

const { task, read, write } = require('taks')
const _postcss = require('postcss')
const _rollup = require('rollup')
const _uglify = require('uglify-es')

const postcss = task.plugin(async function (input, output, options) {
    let opts = Object.assign({ from: undefined, plugins: [] }, options)
    let src = await read(input)
    let { css } = await _postcss(opts.plugins).process(src, opts)
    return write(output, css)
})

const rollup = task.plugin(async function (input, output, options) {
    let opts = Object.assign({ file: output, format: 'iife' }, options)
    let bundle = await _rollup.rollup({ input })
    return bundle.write(opts)
})

const uglify = task.plugin(async function (input, output, options) {
    let src = await read(input)
    let { code } = _uglify.minify({ 'src.js': src }, options)
    return write(output, code)
})

// -----------------------------------------------------------------------------

const cssConfig = require('./postcss.config.js')
const cssMinify = { plugins: ['cssnano'] }

task('styles:main', async function () {
    await postcss('./lib/main.css', './dist/main.css', cssConfig)
})

task('styles:compat', async function () {
    await postcss('./lib/main.css', './dist/main.css', cssConfig)
})

task('styles:min', async function () {
    let conf = { plugins: ['cssnano'] }
    await postcss('./dist/main.css', './dist/main.min.css', conf)
    await postcss('./dist/compat.css', './dist/compat.min.css', conf)
})

task('styles', async function () {
    await task.parallel(['styles:main', 'styles:compat'])
    await task.run('styles:min')
})

task('scripts', async function () {
    await rollup('./lib/main.js', './dist/main.js')
    await uglify('./dist/main.js', './dist/main.min.js')
})

task('build', async function () {
    task.parallel(['styles', 'scripts'])
})

task.run(process.argv[2])