Express is perhaps the most popular Node.js web app framework. It's so popular that it's part of the MEAN Stack acronym. MEAN refers to MongoDB, ExpressJS, AngularJS, and Node.js. Express is described as being Sinatra-like, referring to a popular Ruby application framework, and that it isn't 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.
You can visit the home page for Express at http://expressjs.com/.
Shortly, we'll implement a simple application to calculate Fibonacci numbers using Express, and in later chapters, we'll do ...
