gulpfile.js

var gulp       = require('gulp');
var browserify = require('browserify');
var watchify   = require('watchify');
var babelify   = require('babelify');
var uglifyify  = require('uglifyify');
var source     = require('vinyl-source-stream');
var chalk      = require('chalk');

var inputDir = './src/';
var outputDir = './dist/';

var paths = {
  input: {
    js:      inputDir + '**/*.js',
    jsEntry: inputDir + 'app.js',
    sass:    inputDir + 'style/recommendations.scss',
    html:    inputDir + 'index.html'
  },

  output: {
    css: outputDir + 'recommendations.css'
  }
};

function buildJS(shouldWatch, done) {
  var bundle = function (b, done) {
    console.log(chalk.blue('(re)bundling js'));

    b.transform(babelify);
    b.transform({global: true}, 'uglifyify');

    b.bundle()
      .on('error', function(err) {
        console.log(chalk.red(err.message));
        this.emit('end');
      })
      .pipe(source('recommendations.js'))
      .pipe(gulp.dest(outputDir))
      .on('end', done || function(){});
  };

  var b = shouldWatch ?
    watchify(browserify(watchify.args)) :
    browserify({
      builtins: []
    });

  b.on('update', function() { bundle(b); });
  b.add(paths.input.jsEntry);
  bundle(b, done);
}

gulp.task('watch-js', function (done) {
  buildJS(true, done);
});

gulp.task('build-js', function (done) {
  buildJS(false, done);
});