gulpfile.js

var gulp = require('gulp');
var sass = require('gulp-ruby-sass');
var uglifyjs = require('uglify-es');
var uglify = require('gulp-uglify');
var composer = require('gulp-uglify/composer');
var minify = composer(uglifyjs, console);
var pump = require('pump');
var concat = require('gulp-concat');
var clean = require('gulp-clean');
var gulpSequence = require('gulp-sequence');
var babel = require('gulp-babel');

gulp.task('default', ['sass'], function() {
  gulp.watch("public/css/*.scss", ['sass']);
});

gulp.task('build', gulpSequence('compress', 'merge', 'clean', 'sass'));
gulp.task('dev', ['sass'], function() {
  gulp.watch("public/css/*.scss", ['sass']);
});
 
gulp.task('sass', function(cb) {
    pump([
      sass('public/css/*.scss', {style: 'compressed'}),
      gulp.dest('public/build')
    ], cb);
});

gulp.task('compress', function(cb) {
  var options = {};
  pump([
    gulp.src('public/js/*.js'),
    babel({presets: ['env']}),
    minify(options),
    gulp.dest('public/build/dist')
  ], cb);
});

gulp.task('merge', function(cb) {
  pump([
    gulp.src('public/build/dist/*.js'),
    concat('build.js'),
    gulp.dest('public/build/')
  ], cb);
});

gulp.task('clean', function(cb) {
  pump([
    gulp.src('public/build/dist', {read: false}),
    clean()
  ], cb);
});