gulpfile.js with browserify, reactify, watchify and gulp-notify.

.babelrc

{
  "presets": [ "es2015", "react" ]
}

gulpfile.js

var source = require('vinyl-source-stream');
var gulp = require('gulp');
var gutil = require('gulp-util');
var browserify = require('browserify');
var babelify = require('babelify');
var watchify = require('watchify');
var notify = require("gulp-notify");

var scriptsDir = './scripts';
var buildDir = './build';


function handleErrors() {
  var args = Array.prototype.slice.call(arguments);
  notify.onError({
    title: "Compile Error",
    message: "<%= error.message %>"
  }).apply(this, args);
  this.emit('end'); // Keep gulp from hanging on this task
}


// Based on: http://blog.avisi.nl/2014/04/25/how-to-keep-a-fast-build-with-browserify-and-reactjs/
function buildScript(file, watch) {
  var props = {entries: [scriptsDir + '/' + file], debug: true, cache: {}, packageCache: {}};
  var bundler = watch ? watchify(browserify(props)) : browserify(props);
  bundler.transform(babelify);
  function rebundle() {
    var stream = bundler.bundle();
    return stream.on('error', handleErrors)
    .pipe(source(file))
    .pipe(gulp.dest(buildDir + '/'));
  }
  bundler.on('update', function() {
    rebundle();
    gutil.log('Rebundle...');
  });
  return rebundle();
}


gulp.task('build', function() {
  return buildScript('main.js', false);
});


gulp.task('default', ['build'], function() {
  return buildScript('main.js', true);
});