gulpfile.js

var gulp = require('gulp');

var del = require('del'),
  useref = require('gulp-useref'),
  gulpif = require('gulp-if'),
  htmlmin = require('gulp-htmlmin'),
  mincss = require('gulp-clean-css'),
  uglify = require('gulp-uglify'),
  concat = require('gulp-concat'),
  replace = require('gulp-replace'),
  copy = require('gulp-copy'),
  zip = require('gulp-zip');

var uglifyOpts = {
  compress: {
    global_defs: {
      exports: false,
      define: false
    }
  }
};

gulp.task('clean', function () {
  return del(['dist', 'package.zip']);
});

gulp.task('minify', function () {
  return gulp
    .src('app/*.html')
    .pipe(useref())
    .pipe(gulpif('*.html', htmlmin({ collapseWhitespace: true })))
    .pipe(gulpif('*.css', mincss()))
    .pipe(gulpif('*.js', uglify(uglifyOpts)))
    .pipe(gulp.dest('dist'));
});

gulp.task('opal', function () {
  var base = 'app/lib/opal/opal/' + require('./bower').dependencies.opal;

  return gulp
    .src([base + '/opal.js', base + '/opal-parser.js', 'app/js/override.js'])
    .pipe(concat('opal.js'))
    .pipe(uglify())
    .pipe(gulp.dest('dist/js'));
});

gulp.task('worker', function () {
  return gulp
    .src('app/js/worker.js')
    .pipe(
      replace(/importScripts\([^)]+\);/m, 'importScripts("../js/opal.js");')
    )
    .pipe(uglify())
    .pipe(gulp.dest('dist/js'));
});

gulp.task('copy', function () {
  return gulp
    .src(['app/img/**/*', 'app/manifest.webapp'])
    .pipe(copy('dist', { prefix: 1 }));
});

gulp.task(
  'package',
  gulp.series(
    'clean',
    gulp.parallel('minify', 'worker', 'opal', 'copy'),
    function () {
      return gulp
        .src('dist/**/*')
        .pipe(zip('package.zip'))
        .pipe(gulp.dest('.'));
    }
  )
);

gulp.task('default', gulp.series('package'));