gulpfile.babel.js

var gulp = require('gulp');
var browserify = require('browserify');
var gutil = require('gulp-util');
var tap = require('gulp-tap');
var buffer = require('gulp-buffer');
var sourcemaps = require('gulp-sourcemaps');

gulp.task('sets', function () {
  return gulp.src('src/engine/cards/sets/**/set.js', {read: false}) // no need to read file because browserify does it
    // transform file objects using gulp-tap plugin
    .pipe(tap(function (file) {
      gutil.log('bundling ' + file.path);
      // replace file contents with browserify's bundle stream
      file.contents = browserify(file.path, {debug: true}).bundle();
    }))
    // transform streaming contents into buffer contents (because gulp-sourcemaps does not support streaming contents)
    .pipe(buffer())
    .pipe(sourcemaps.init({loadMaps: true}))
    // .pipe(uglify())
    .pipe(sourcemaps.write('./'))
    .pipe(gulp.dest('src/simplefrontend/js/bundles'));
});