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JavaScript Introduction

JavaScript is the programming language of the web. It runs in every browser to make pages interactive, and — via Node.js — on servers, desktops, and everywhere else too. It's one of the most widely-used languages in the world.

What kind of language it is

Dynamically typed — variables don't declare a type; values carry it at runtime.
Multi-paradigm — supports functional *and* object-oriented styles.
Single-threaded with an async model — one main thread, but non-blocking I/O via an event loop.
Interpreted / JIT-compiled — no separate build step needed to run it.

JavaScript vs ECMAScript

ECMAScript (ES) is the *specification*; JavaScript is the language that implements it. “ES6” / “ES2015” and the yearly releases since (ES2016…ES2024) added the modern features — let/const, arrow functions, classes, modules, async/await — that this course uses throughout.

Where it runs

concept

Browser  ->  interactivity, the DOM, fetch, events
Node.js  ->  servers, CLIs, build tools, scripts
# same language, different available APIs

Why learn core JavaScript

Note: Nearly the entire modern web stack is *built on* JavaScript — TypeScript is JS plus types, and React, Angular, Node.js, and Express are all JavaScript. Solid core JS makes every one of those far easier; shaky fundamentals make all of them harder.

Tip: Focus on the fundamentals first — values and types, functions and closures, arrays and objects, and the async model. They're the foundation everything else builds on. This course covers them, then the browser APIs (DOM, events, fetch) and modern features that turn core JS into real-world web development.

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