Introduction
Welcome to the JavaScript handbook! I'm Juno, and I love teaching this one. HTML gives a page its structure and CSS gives it a look, and JavaScript is what makes it actually do things: respond to a click, update the page, fetch new data.
We'll start from the very first line of code and build up slowly, one idea at a time. No experience needed, and nothing here is ever too basic to ask about.
Take it at your own pace and we'll get there together!
This handbook is for anyone learning to program for the web. JavaScript is the language that runs in every browser, and it is what turns a static page into something that reacts: it responds when you click a button, checks a form before it sends, updates part of the page without a reload, and pulls in fresh data from a server. HTML says what is on the page and CSS says how it looks; JavaScript says what it does. A quick word on two terms you'll see throughout: a value is a single piece of data, like the number 42 or the text "hello", and a variable is a name you give a value so you can use it later. Every concept here is written out in full, with depth, examples, and something to search whenever you need a quick answer.
You do not need any prior coding experience to start. If you have written a little HTML, you have more than enough, and everything else is introduced as it comes up. JavaScript is where most web developers first learn to actually program, because it is the one language the browser runs directly.
The handbook works its way from the ground up. You'll learn how to store and change values, how to make decisions and repeat work, how to organise code into functions, how to hold collections of data in arrays and objects, and then how to reach into a web page to read and change it, respond to what the user does, and load data without a page refresh. Each idea is small on its own, and they stack into pages that actually do something.
The approach here is to explain what each piece of JavaScript does and why, not only what to type. Anyone can copy a snippet and watch it run once. The distance between that and writing code you can read, trust, and change six months later is understanding what the language is actually doing when it runs. That understanding is what outlasts any single project.
A word on scope, so you know what this handbook is and is not. JavaScript is a large language, and no single set of docs covers all of it. What you will learn here is the foundation: the core you reach for in almost every piece of JavaScript you write, from your first script to a real application. It goes as far as loading data from a server, which is where a lot of introductions stop. Beyond it lie the tools and libraries built on top of these same fundamentals, frameworks like React, running JavaScript outside the browser with Node, adding types with TypeScript. Get the foundation solid and the rest is a much shorter climb.
Meet your guides
This handbook is hosted by three guides, and you pick which one shows you around. The material is the same for everyone; your guide sets the voice it is told in, and on the pages that adapt, how deep each section goes.
- Juno teaches the beginner track: warm and patient, plain analogies, nothing assumed.
- Ace teaches the intermediate track: practical and build-first, straight to what you actually do.
- Sol teaches the Deep Dive: the mechanism, the trade-offs, and the production details everyone else skips.
Switch guide any time from the picker at the top of any page, or open Preferences at the bottom right to change your guide, language, or font size.
When you're set, the handbook starts in earnest. The next chapter, What is JavaScript, covers what JavaScript really is, where it runs, and how it fits alongside the HTML and CSS you already know.
Prefer to learn by building?Scrimba's free 9-hour JavaScript course builds a passenger counter, a Blackjack game, a Chrome extension, and a mobile app, with interactive challenges throughout.