What is JavaScript?

JavaScript is a high-level, dynamically-typed programming language that runs natively in every web browser and, via Node.js, on servers too. Created in 1995 to make static web pages interactive, it's now one of the three core web technologies alongside HTML (structure) and CSS (style) — JavaScript adds behavior: responding to clicks, updating content without a page reload, validating forms, and talking to servers.

console.log("Hello, world!");

JavaScript engines — V8 in Chrome and Node.js, SpiderMonkey in Firefox, JavaScriptCore in Safari — parse and execute this code directly, with no separate compile step needed from the developer's side.

JavaScript follows the ECMAScript specification, maintained by TC39, and the language keeps evolving on a yearly release cycle. "Modern JavaScript" generally means ES2015 (ES6) and later, which introduced classes, arrow functions, let/const, promises, and modules. This notebook uses up-to-date syntax throughout, including features from ES2020 through ES2024.