To perform TDD in JavaScript for a modern web application, we absolutely need Node. When writing a modern web application, you will very likely be using one of these popular frameworks: ReactJS, Angular, Ember.js, Vue.js, or Polymer. The majority of these applications require a compilation step in Node.

Another reason for using Node is that we want to take advantage of new features in JavaScript. Node doesn’t support these features itself, but libraries have been written that will allow you to transpile the newer versions of JavaScript, ECMAScript 2015+, into a version of JavaScript that is supported by your target browsers.

Lastly, we need Node so that we can run our tests. Later, we will discuss how we can also run our tests continuously while we are writing our code. This is known as continuous testing and is a must-have for rapid development.