A lot of developers coming to JavaScript world attracted by React.js are confused with the tooling used to produce modern JavaScript code. Webpack, Babel, ESLint, Mocha, Karma, Grunt... what should I use and which tool is doing what? JavaScript newcomers are often people coming from communities like Ruby and Java where opinionated, full-stack solutions exist. Frameworks like Ruby on Rails provide a lot of features out of the box - in fact the problem you may have with JavaScript is caused by that. You do not think about the building tools for your code - your template language processors, asset pipeline, cache middleware and a lot other things are pre-configured for you and they work transparently. JavaScript tooling often consists of small tools, utilities and libraries that combined builds your code to be used in a browser. They allow you to rebuild your project after changes, run your test suite, hot reload your code and so on. You may be lost in this world - I was lost when I first tried to build my JavaScript stack for working with ES2015 code. In fact this is a problem that you wish to have - system composed of small parts is much more maintainable and flexible than a big monolith that popular framework provides to you. But starting with such granular tooling can be hard. I'd like to give you a quick overview about what popular tools do - and whether you need them or not.