Gulpfile that compiles with Babel

gulpfile.js

/*
 * Copyright 2016 Google Inc. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

const gulp = require('gulp');
const browserify = require('browserify');
const source = require('vinyl-source-stream');
const buffer = require('vinyl-buffer');
const babel = require('gulp-babel');

gulp.task('scripts', function() {
  return browserify({
    entries: 'index.js',
  }).bundle()
  .pipe(source('index-compiled.js'))
  .pipe(buffer())  // turns this into a "real file", and not a stream
  .pipe(babel({
    presets: ['es2015'],   // es2015 specifies const, let, etc
  }))
  .pipe(gulp.dest('./'));
});

gulp.task('default', ['scripts']);