Express is perhaps the most popular Node.js web app framework. Express is described as being Sinatra-like, which refers to a popular Ruby application framework. It is also regarded as not being an opinionated framework, meaning the framework authors don't impose their opinions about structuring an application. This means Express is not at all strict about how your code is structured; you just write it the way you think is best.
As of the time of writing this book, Express 4.17 is the current version, and Express 5 is in alpha testing. According to the Express.js website, there are very few differences between Express 4 and Express 5.
Let's start by installing express-generator. While we can just start with writing some code, express-generator provides a blank starting application, which we'll take and modify.
Install express-generator using the following commands:
$ mkdir fibonacci...
