gulpfile.js

const gulp      = require('gulp');
const sass      = require('gulp-sass');
const sassGlob  = require('gulp-sass-glob');
const sourcemaps = require('gulp-sourcemaps');
const gutil     = require('gulp-util');
const notify    = require('gulp-notify');
const browserify = require('browserify');
const watchify  = require('watchify');
const babelify  = require('babelify');
const source    = require('vinyl-source-stream');
const buffer    = require('vinyl-buffer'); 

const production = process.env.ENV === 'prod';

function handleError () {
  const args = Array.prototype.slice.call(arguments);
  notify.onError({
    title: "Compile Error",
    message: "<%= error.message %>"
  }).apply(this, args);
  this.emit('end');
}

function css () {

  function rebuild () {
    console.log('-> Building css');
    gulp.src('./app/assets/stylesheets/**/app.scss')
      .pipe(sourcemaps.init())
      .pipe(sassGlob())
      .pipe(sass({ errLogToConsole: true }))
      .on('error', function (err) {
        console.log(err.message)
        this.emit('end');
      })
      .pipe(sourcemaps.write())
      .pipe(gulp.dest('public/css/'))
      .pipe(notify('Built css'));
  }

  gulp.watch('./app/assets/stylesheets/**/*.scss', rebuild);

  rebuild();
}

function js (watch) {
  const src = './app/assets/scripts';
  const opts = {
    entries: [`${src}/app.js`],
    debug: false
  }
  
  const bundler = watch ? watchify(browserify(opts)) : browserify(opts);
  bundler.transform(babelify);

  function rebuild () {
    const start = Date.now();
    gutil.log('Compiling javascript');

    bundler
    .bundle()
    .on('error', handleError)
    .pipe(source('bundle.js'))
    .pipe(buffer())
    .pipe(gulp.dest('./public/javascripts/'))
    .pipe(notify('Compiled javascript'));

    gutil.log(`Done, time spent: ${Date.now() - start} ms.`);
  }

  bundler.on('update', rebuild);
  rebuild();
}

gulp.task('css', () => css());
gulp.task('js', () => js());

gulp.task('watch', () => {
  css(true);
  js(true);
});

gulp.task('build', ['css', 'js'])
gulp.task('default', ['watch']);