Modern apps have several requirements, which cannot be provided by the app itself, such as central data storage, communication routing, and user management. In order to provide such services, apps rely on an external software component known as the backend. The backend will be executed on one or more remote servers, listen to network requests from the devices that run the app, and provide them with the services that requests require.

The backend that we will use in this book is Node.js, a powerful but strange beast in its category. Node.js, at the time of writing this book, is the only major backend that is written almost entirely in JavaScript, which in reality is a frontend scripting language. The creators of Node.js wanted a backend that could be integrated with the apps written in JavaScript as seamlessly as possible, and you cannot get much closer to that than Node.js. Beyond this, Node.js is known for being both reliable and high-performing.

In terms of architecture, Node.js is highly modularized and designed from the ground up to be extendable through plugins or packages. Node.js comes with its own package management system, Node Package Manager (NPM), through which you can easily install, remove, and manage packages for your project. You will see how to use NPM in order to install other necessary components later in this chapter.