gulpfile.js

var gulp = require('gulp'),
	babel = require('gulp-babel'),
	concat = require('gulp-concat'),
	uglify = require('gulp-uglify'),
	plumber = require('gulp-plumber'),
	sass = require('gulp-sass')(require('sass'))

var settings_js_compiler = {
	compact: false,
	presets: [
		'@babel/env'
	]
}

var settings_sass_compiler = {
	comments: false,
	outputStyle: 'compressed'
}

gulp.task('sass-compiler', e => {
	return gulp.src(
		'./assets/sass/**/*.{scss, sass}'
	).pipe(
		sass.sync(
			settings_sass_compiler
		).on(
			'error', sass.logError
		)
	).pipe(
		gulp.dest('./assets/css/')
	)
})

gulp.task('app', e => {
	return gulp.src([
		'./assets/js/app/**/*.js'
	]).pipe(
		plumber()
	).pipe(
		babel(settings_js_compiler)
	).pipe(
		uglify()
	).pipe(
		concat('app.js')
	).pipe(
		uglify()
	).pipe(
		gulp.dest('./assets/js/')
	)
})

gulp.task('engine', e => {
	return gulp.src([
		'./assets/js/engine/**/*.js'
	]).pipe(
		plumber()
	).pipe(
		babel(settings_js_compiler)
	).pipe(
		uglify()
	).pipe(
		concat('engine.js')
	).pipe(
		uglify()
	).pipe(
		gulp.dest('./assets/js/')
	)
})

gulp.task('plugins', e => {
	return gulp.src([
		'./assets/js/plugins/**/*.js'
	]).pipe(
		plumber()
	).pipe(
		babel(settings_js_compiler)
	).pipe(
		uglify()
	).pipe(
		concat('plugins.js')
	).pipe(
		uglify()
	).pipe(
		gulp.dest('./assets/js/')
	)
})

gulp.task('gui', e => {
	return gulp.src([
		'./assets/js/gui/**/*.js'
	]).pipe(
		plumber()
	).pipe(
		babel(settings_js_compiler)
	).pipe(
		uglify()
	).pipe(
		concat('gui.js')
	).pipe(
		uglify()
	).pipe(
		gulp.dest('./assets/js/')
	)
})

gulp.task('sass', e => {
	gulp.watch([
		'assets/sass/**/*.{scss, sass}'
	], gulp.parallel([ 
		'sass-compiler' 
	]))
})

gulp.task('js', e => {
	gulp.watch([
		'assets/js/**/*.js', 
		'!assets/js/apis/**/*.js'
	], gulp.parallel([ 
		'app', 
		'engine',
		'plugins',
		'gui' 
	]))
})