Languages

The DOM (Document Object Model) is a tree representation of an HTML page. JavaScript can read it, modify it, add to it, and remove from it — which is how every interactive web page works. document.querySelector, createElement, appendChild, addEventListener — these are the tools. Key point: The DOM is a live tree. When you change…

Events are the nervous system of a web page. Every click, keystroke, scroll, and network response fires an event, and JavaScript listens. Understanding events — how they propagate, how to listen, how to stop them, and how to delegate — is what separates a static page from a responsive application. The core of it is…

The browser gives JavaScript more than just the DOM. It exposes a set of Web APIs — tools the environment provides on top of the language — for talking to servers, storing data, and scheduling work. Three of them cover the vast majority of what you’ll do in real code: fetch for network requests, localStorage…

Design patterns are reusable solutions to common problems. They’re not algorithms — they’re templates for structuring code that have proven themselves across many projects. In JavaScript, some patterns are more relevant than others because the language handles certain things natively. The patterns worth knowing in JavaScript fall into three groups: creational (how to make objects),…

JavaScript manages memory for you. You create objects, arrays, and closures — and the engine reclaims them when they’re no longer needed. That’s the deal. In exchange, you can’t manually free memory, and you can’t force garbage collection. But you can create leaks, and you can prevent them. Understanding how garbage collection works isn’t about…

Some events fire hundreds of times per second. Scroll, resize, mousemove, input — the browser doesn’t wait for the user to pause; it fires a callback on every change. If your handler does real work, that’s hundreds of times more work than necessary. Debounce and throttle are the two patterns that fix this. They both…

Testing is how you prove your code works — and how you keep it working as it changes. Without tests, every edit is a gamble. With tests, you can refactor confidently, catch regressions immediately, and document what the code is supposed to do. JavaScript has a mature testing ecosystem, and the concepts are the same…

For most of JavaScript’s life, it ran only in the browser. Node.js changed that. It takes the V8 engine — the same one inside Chrome — and wraps it with an environment that can read files, open sockets, spawn processes, and run on servers. Suddenly JavaScript could do what PHP, Python, and Ruby did. Node…

Every Node project has a package.json. It’s the manifest — the file that describes your project, lists its dependencies, and defines scripts. Around it, a package manager installs, updates, and resolves those dependencies. Three tools dominate the ecosystem: npm, yarn, and pnpm. They do the same job with different trade-offs. Understanding package.json and how the…

JavaScript doesn’t stop moving. Every year, TC39 ships new features — some big, some small, all designed to remove boilerplate and fix sharp edges. Between ES2022 and the latest proposals, a set of methods and syntax has landed that most developers haven’t caught up with yet. This chapter covers what’s actually in the language now,…