JavaScript Essentials

JavaScript is the language of Node.js

Node.js is a runtime that executes JavaScript outside the browser. Everything you write in Node — from a simple HTTP server to a complex CLI tool — is JavaScript. That means a solid grip on the language itself is non-negotiable before diving into Node’s APIs.

This module covers the JavaScript fundamentals that trip up developers most in the Node ecosystem:

Lesson	Topic
Types and Coercion	Primitives vs objects, `typeof`, `==` vs `===`, truthy/falsy
Scope and Closures	`var`/`let`/`const`, block scope, hoisting, lexical scope
`this` and Context	Dynamic `this`, `call`/`apply`/`bind`, arrow functions
Modules	ESM `import`/`export` vs CommonJS `require`, when to use each

Modern JavaScript means ES2022 and later throughout — const/let, arrow functions, destructuring, async/await, optional chaining, and native ES modules. This module uses Node 20+.

A first runnable demo

The snippet below demonstrates several JS concepts at once: a const declaration, a function, a template-string-free concatenation, and a closure over the outer variable. Run it and inspect the output.

const greet = function(name) {
  return 'Hello, ' + name + '!';
};

const languages = ['JavaScript', 'TypeScript', 'Node.js'];

for (const lang of languages) {
  console.log(greet(lang));
}

JavaScript

const greet = function(name) {
  return 'Hello, ' + name + '!';
};

const languages = ['JavaScript', 'TypeScript', 'Node.js'];

for (const lang of languages) {
  console.log(greet(lang));
}

What does Node.js provide that a browser does not? A JavaScript engine Access to the file system, network sockets, and OS APIs without a browser sandbox Support for `const` and `let` Garbage collection

Which JavaScript version features does this module rely on? ES5 only — for maximum compatibility ES2015 (ES6) only ES2022 and later, running on Node 20+ TypeScript — which is compiled down to ES3