Gulpfile.js

const gulp = require('gulp'),
  gulpif = require('gulp-if'),
  clean = require('gulp-clean'),
  browserSync = require('browser-sync'),
  reloadMe = require('browser-sync').reload,
  imageMin = require('gulp-imagemin'),
  sourcemaps = require('gulp-sourcemaps'),
  ngAnnotate = require('gulp-ng-annotate'),
  babel = require('gulp-babel'),
  concat = require('gulp-concat'),
  uglify = require('gulp-uglify'),
  stylus = require('gulp-stylus'),
  cssMin = require('gulp-minify-css'),
  nib = require('nib'),
  es = require('event-stream'),
  merge = require('event-stream').concat;

const publicDir = __dirname + '/public',
  publicImgDir = __dirname + '/public/img';

const concatAppJS = function (minifyMe) {
  const stream = gulp
    .src(['./assets/scripts/App.js', './assets/scripts/**/*.js'])
    .pipe(gulpif(minifyMe, ngAnnotate()))
    .pipe(sourcemaps.init())
    .pipe(babel());

  stream.on('error', function () {
    console.log('Error parsing JS!');
  });

  return stream.pipe(concat('app.js')).pipe(gulpif(minifyMe, uglify())).pipe(gulp.dest(publicDir));
};
const concatVendorJS = function (minifyMe) {
  return gulp
    .src([
      './bower_components/jquery/dist/jquery.js',
      './bower_components/highcharts-release/highcharts.js',
      './bower_components/angular/angular.js',
    ])
    .pipe(concat('vendor.js'))
    .pipe(gulpif(minifyMe, uglify()))
    .pipe(gulp.dest(publicDir));
};
const concatCSS = function (minifyMe) {
  return gulp
    .src(['./assets/styles/reset.styl', './assets/styles/main.styl'])
    .pipe(stylus({use: [nib()]}))
    .pipe(concat('app.css'))
    .pipe(gulpif(minifyMe, cssMin()))
    .pipe(gulp.dest(publicDir))
    .pipe(reloadMe({stream: true}));
};
const copyStuff = function () {
  return gulp.src('./assets/img/**/*', {base: './assets'}).pipe(filterEmptyDirs()).pipe(gulp.dest(publicDir));
};

//removes empty dirs from stream
const filterEmptyDirs = function () {
  return es.map(function (file, cb) {
    if (file.stat.isFile()) {
      return cb(null, file);
    } else {
      return cb();
    }
  });
};

const minifyImages = function () {
  return gulp
    .src(publicImgDir + '/**/*')
    .pipe(imageMin())
    .pipe(gulp.dest(publicImgDir));
};

//opens up browserSync url
const syncMe = function () {
  browserSync({
    proxy: 'localhost:8000',
    open: false,
  });
};

//cleans build folder
gulp.task('clean', function () {
  console.log('Cleaning:', publicDir);
  return gulp.src(publicDir, {read: false, allowEmpty: true}).pipe(clean());
});

//build + watching, for development
gulp.task(
  'default',
  gulp.series('clean', function () {
    gulp.watch(['./assets/scripts/**/*.js'], function () {
      console.log('File change - concatAppJS()');
      concatAppJS().pipe(reloadMe({stream: true}));
    });
    gulp.watch('./assets/styles/**/*.styl', function () {
      console.log('File change - concatCSS()');
      concatCSS();
    });
    gulp.watch(['./assets/img/**/*'], function () {
      console.log('File change - copyStuff()');
      copyStuff().pipe(reloadMe({stream: true}));
    });
    gulp.watch(['./app/views/**/*'], function () {
      console.log('File change - templates');
      reloadMe();
    });

    return merge(copyStuff(), concatCSS(), concatAppJS(), concatVendorJS()).on('end', function () {
      syncMe();
    });
  })
);

gulp.task(
  'watch',
  gulp.series('default', function () {
    gulp.watch(['./assets/scripts/**/*.js'], function () {
      console.log('File change - concatAppJS()');
      concatAppJS().pipe(reloadMe({stream: true}));
    });
    gulp.watch('./app/styles/**/*.styl', function () {
      console.log('File change - concatCSS()');
      concatCSS();
    });
    gulp.watch(['./assets/img/**/*'], function () {
      console.log('File change - copyStuff()');
      copyStuff().pipe(reloadMe({stream: true}));
    });
  })
);

//production build task
gulp.task(
  'build',
  gulp.series('clean', function (done) {
    return merge(copyStuff(), concatCSS(true), concatAppJS(true), concatVendorJS(true)).on('end', function () {
      minifyImages().on('end', done);
    });
  })
);