gulpfile.js

var gulp = require('gulp');
var sass = require('gulp-sass');
var rename = require('gulp-rename');
var babel = require('babelify');
var browserify = require('browserify');
var source = require('vinyl-source-stream');
var watchify = require('watchify');

gulp.task('styles', function () {
	gulp
		.src('index.scss')
		.pipe(sass())
		.pipe(rename('app.css'))
		.pipe(gulp.dest('public'));
})

gulp.task('assets', function () {
	gulp
		.src('assets/*')
		.pipe(gulp.dest('public'));
})

function compile(watch) {
	var bundle = watchify(browserify('./src/index.js'))

	function rebundle() {
		bundle
			.transform(babel)
			.bundle()
			.on('error', function (err) { console.log(err); this.emit('end') })
			.pipe(source('index.js'))
			.pipe(rename('app.js'))
			.pipe(gulp.dest('public'));
	}
	if (watch) {
		bundle.on('update', function () {
			console.log('---> Bundling...');
			rebundle();
		})
	}

	rebundle();
}

gulp.task('build', function () {
	return compile();
});

gulp.task('watch', function () { return compile(true); });

gulp.task('default', ['styles', 'assets', 'build']);