ES6 project with Babel, Browserify & Gulp

gulpfile.js

'use strict';

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

function compile (watch) {
  var filename = watch ? 'app-dev.js' : 'app.js';
  var bundler = browserify('./app.js', { debug: true }).transform(babel)
  var watcher = watch ? watchify(bundler) : '';

  function rebundle () {
    return bundler.bundle()
      .on('error', function(err) { console.error(err); this.emit('end'); })
      .pipe(source(filename))
      .pipe(buffer())
      .pipe(sourcemaps.init({ loadMaps: true }))
      .pipe(sourcemaps.write('./'))
      .pipe(gulp.dest('./dist'));
  }

  if (watch) {
    watcher.on('update', function () {
      console.log('-> bundling...');
      rebundle();
    });
  }

  return rebundle();
}

function watch() {
  return compile(true);
};

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

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