Install all dependencies:
npm install babel-preset-es2015 babelify babelify-es6-polyfill babelify browserify handlebars jquery watchify
Modify any file within the JS folder (do not alter bundle.js) and recompile bundle.js using:
browserify js/app.js -t babelify -o bundle.js
During development you might want to automatically recompile the bundle using:
watchify js/app.js -t babelify -o bundle.js