Too Long; Didn't Read
One of the main reasons for using Node.js is that you can create quickly RESTful web APIs with it. Express is a popular web framework helping you with this task. Using JavaScript to build servers is often a natural choice for frontend developers looking for a way to reuse their skills and create the APIs supporting their web app, but that's not the only benefit of using Node.js. The huge package ecosystem around Node.js and Express is what makes it shine, allowing to implement a lot of business features with very few lines of code.