Node.js is an event-driven, server-side JavaScript environment. Node.js runs JS using the V8 engine developed by Google for use in their Chrome web browser. Leveraging V8 allows Node.js to provide a server-side runtime environment that compiles and executes JS at lightning speeds.

Node.js runs as a single-threaded process that acts upon callbacks and never blocks on the main thread, making it high-performing for web applications. A callback is basically a function that is passed to another function so that it can be called once that function is done. We will look into this in a later topic. This is known as the single-threaded event loop model. Other web technologies mainly follow the multithreaded request-response architecture.

The following diagram depicts the architecture of Node.js. As you can see, it's mostly C++ wrapped by a JavaScript layer. We will not go over the details of each component, since that is out of the scope of this chapter.

Node's goal is to offer an easy and safe way to build high-performance and scalable network applications in JavaScript.

Node.js has the following four major applications:

• Creating REST APIs: We are going to look into this more in subsequent chapters
• Creating real-time services: Because of Node's asynchronous event-driven programming, it is well-suited to reactive real-time services
• Building microservices: Since Node.js has a very lean core, it is best suited to building microservices, since you will only add dependencies that you actually need for the microservices, as opposed to the glut that comes with other frameworks
• Tooling: For example, DevOps automations, and so on

Before You Begin

Open the IDE and the Terminal to implement this solution.

Aim

Learn how to write a basic Node.js file and run it.

Scenario

You are writing a very basic mathematical library with handy mathematical functions.

Steps for Completion

1. Create your project directory (folder), where all the code for this and other chapters will be kept. You can call it beginning-nodejs for brevity. Inside this directory, create another directory named lesson-1, and inside that, create another directory called activity-a. All this can be done using the following command:

mkdir -p beginning-nodejs/lesson-1/activity-a

2. Inside activity-a, create a file using touch maths.js command.  
3. Inside this file, create the following functions:
   • add: This takes any two numbers and returns the sum of both, for example, add(2, 5) returns 7
   • sum: Unlike add, takes any number of numbers and returns their sum, for example, sum(10, 5, 6) returns 21
4.  After these functions, write the following code to act as tests for your code:

console.log(add(10, 6)); // 16
console.log(sum(10, 5, 6)); // 21

5. Now, on the Terminal, change directory to lesson-1. That's where we will be running most of our code from for the whole chapter.
6. To run the code, run the following command:

node activity-a/math.js

The 16 and 21 values should be printed out on the Terminal.