gulpfile.js

// Load some modules which are installed through NPM.
var gulp = require('gulp');
var browserify = require('browserify');  // Bundles JS.
var reactify = require('reactify');  // Transforms React JSX to JS.
var source = require('vinyl-source-stream');

// Define some paths.
var paths = {
  app_js: ['./example/src/app.jsx'],
  js: ['example/src/*.*'],
};

// Our JS task. It will Browserify our code and compile React JSX files.
gulp.task('js', function() {
  // Browserify/bundle the JS.
  browserify(paths.app_js)
    .transform(reactify)
    .bundle()
    .pipe(source('bundle.js'))
    .pipe(gulp.dest('./example/build/'));
});

// Rerun tasks whenever a file changes.
gulp.task('watch', function() {
  gulp.watch(paths.js, ['js']);
});

// The default task (called when we run `gulp` from cli)
gulp.task('default', ['watch']);