How to Set up a React-Based Application

React is a JavaScript library, so we should be able to make a reference to it through a <script> tag in our HTML page and start writing our web application. However, this approach would prevent us from exploiting some features that are provided by a modern JavaScript development environment—features that make our lives easier. For example, we wouldn't be able to use recent features from ECMAScript 2015+, such as classes, modules, arrow functions, let and const statements, and so on. Or, we could use those features, but only recent browsers would support them.