Understanding Node.js

What is Node.js?

Originally, JavaScript could only be run inside the browser, limiting what it could do.

With Node.js, JavaScript could be used server-side, allowing devs to create:

• Web servers

• Command line interfaces

• Application backends

• And more

How is it possible to run JavaScript server-side?

According to the Node.js website, Node.js is a JavaScript runtime built on Chrome's V8 JavaScript engine. Let's break that down.

A JavaScript engine takes in JavaScript code and compiles it down to machine-readable code. Chrome's V8 JavaScript engine does this for Chrome browsers. All browsers each have their own engine. Node.js leverages the V8 JavaScript engine to perform compilation.

Note: The V8 engine is written in C++. So is Chrome and Node.js!

Node.js is a JavaScript runtime: something that provides tools and libraries specific to the Node.js environment. In the browser, its runtime includes things like the window object and document object (for DOM manipulation). In Node.js, these tools and libraries include the fs (filesystem) and os objects. They allow you to do things like:

• Set up web servers

• Integrate with file systems for reading and writing

These special tools in Chrome and Node.js are written in C++. They're what allow you to manipulate the DOM or file systems (respectively), even though these features aren't technically built into JavaScript. They are called bindings. For example, document.querySelector in Chrome is binded to a C++ function written in Chrome. So is fs.readFile in Node.js.

In contrast, things like the String and Number prototypes are provided directly by the V8 engine itself, not Node.js or the browser. They're what allow you to do things like "Dan Fitz".length or 2 + 3.

Pro tip: You can access Node.js API bindings in their docs.

Differences between browser and Node.js

Node.js comes with these objects and more:

• global is closest to window in the browser: it provides the initial execution context with tons of built-in properties and methods.

• process is closest to document: it gives us the ability to manipulate the Node process running.

  • Example: process.exit() exits the Node.js REPL.

Why Should I Use Node.js?

Furthering the description of Node.js on their site:

Node.js uses an event-driven, non-blocking I/O model that makes it lightweight and efficient. Node.js package ecosystem, npm, is the largest ecosystem of open source libraries in the world.

Event-driven non-blocking I/O model

When Node.js reads data from a file or queries data from a database, it's performing an I/O operation. It's sending a request or input and receives data or an output back.

The nature of I/O is that it takes time to perform. That's why Node.js is non-blocking: while waiting for a response, it can continue to run code.

Pro tip: An extra feature of non-blocking runtimes like Node.js is that they overlap I/O operations. If I send 2 database queries, they can run concurrently in the background.

These 2 database queries are often given callbacks, which execute when the data is returned. Just like the event queue in the browser, that's why Node.js is event-driven.

Example:

// The callback runs when the query is complete
getUser(1, user => console.log(user));

npm

Node.js makes npm possible. (I suppose because of its ability to create CLIs and its ability to read and write files in file systems.) Because npm is such a huge package manager, it's an incredible resource that can solve almost anything.