gulpfile.babel.js

import gulp from 'gulp';
import sass from 'gulp-sass';
import babel from 'gulp-babel';
import sourcemaps from 'gulp-sourcemaps';
import es from 'event-stream';
import rename from 'gulp-rename';
import uglify from 'gulp-uglify';

const sassOpts = {outputStyle: 'compressed', errLogToConsole: true};

let riseError = (err) => {
	console.log(err.toString());
	this.emit('end');
};

gulp.task('sass', () => {
	gulp.src('./css/*.scss')
		.pipe(sass(sassOpts))
		.pipe(gulp.dest('./css'));
});

gulp.task('babel', () => {
	return es.concat(
		gulp.src('./js/*.es')
			.pipe(sourcemaps.init())
			.pipe(babel({presets: ['es2015']}))
			.on('error', riseError)
			.pipe(gulp.dest('./js'))
			.pipe(uglify())
			.pipe(rename((path) => path.extname = '.min.js'))
			.pipe(sourcemaps.write('.'))
			.pipe(gulp.dest('./js'))
	);
});

gulp.task('watch', () => {
	gulp.watch('./css/*.scss', ['sass']);
	gulp.watch('./js/*.es', ['babel']);
});

gulp.task('default', ['sass', 'babel', 'watch']);