Node.js Fundamentals and Runtime

Understand what Node.js is, how it works, why it is different from browser JavaScript, and how to build and execute your first Node.js programs.

What Is Node.js?

Node.js is a JavaScript runtime built on the V8 JavaScript engine. It allows JavaScript to execute outside the browser, making it possible to build servers, APIs, command-line tools, background workers, automation scripts, and real-time applications.

Unlike browser JavaScript, Node.js provides APIs for operating-system and server-side capabilities such as the file system, networking, processes, environment variables, streams, and TCP sockets.

Node.js is especially effective for I/O-heavy workloads because applications can initiate asynchronous operations without blocking the JavaScript execution thread.

Runtime vs Language

JavaScript is the language. Node.js is a runtime that provides an environment and APIs for executing JavaScript outside the browser.

Node.js Runtime Overview

Your First Node.js Program

console.log('Hello from Node.js');

💡 Save the file as app.js and execute it with node app.js. Node.js runs the JavaScript without requiring a browser.

Key Takeaways

Node.js is a JavaScript runtime, not a new programming language.
Node.js is powered by V8 and provides server-side APIs through the Node.js runtime.
Its asynchronous architecture makes it well suited to I/O-heavy applications.

Knowledge Check

What is Node.js?

Installing Node.js and Using the Node CLI

The node command is the primary CLI for executing JavaScript files and interacting with the Node.js runtime. You can verify your installation using node --version and npm --version.

Node also provides a REPL, which is useful for experimenting with JavaScript and Node APIs interactively.

Use a Version Manager

Using a Node.js version manager such as nvm makes it easier to switch between Node.js versions for different projects.

Node.js CLI Basics

node --version
npm --version
node
node app.js

💡 The first two commands display installed versions, node starts the REPL, and node app.js executes a JavaScript file.

Key Takeaways

Use node filename.js to execute a Node.js application.
The Node REPL is useful for quickly testing JavaScript expressions.
Keep project Node.js versions consistent across development and production.

Knowledge Check

Which command executes `server.js`?

Global Objects and the Process Object

Node.js provides useful global objects and variables such as process, console, Buffer, setTimeout, and globalThis. The process object provides information and controls for the currently running Node.js process.

Common properties include process.env for environment variables, process.argv for command-line arguments, and process.exit() for terminating a process.

Working with process

console.log('Arguments:', process.argv.slice(2));
console.log('Environment:', process.env.NODE_ENV || 'development');
console.log('PID:', process.pid);

💡 This example reads command-line arguments, accesses an environment variable, and prints the process ID.

Key Takeaways

Use process.env for runtime configuration.
Use process.argv to access command-line arguments.
Avoid hardcoding secrets directly in source code.

Knowledge Check

Where are environment variables accessed in Node.js?

What Is Node.js?

Installing Node.js and Using the Node CLI

Global Objects and the Process Object

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