Basic JavaScript

What is JavaScript?

JavaScript is the programming language of the web — every interactive thing a website does, from validating a form to updating content without reloading the page, is written in it. Beyond the browser, the same language now runs servers, mobile apps, and command-line tools, which makes it one of the most widely used programming languages in the world.

Why learn it?

Because it’s everywhere, JavaScript is one of the most practical languages to know: it’s the only language that runs natively in every web browser, it has an enormous ecosystem of libraries and tools, and the syntax skills you build here carry over directly into frameworks, back-end services, and even other C-style languages. Whether you want to build websites, apps, or just understand how the software around you works, the essentials in this series are the foundation everything else is built on.

How this series works

Each lesson focuses on a single piece of JavaScript syntax. Inside you’ll find:

• An introduction explaining what the syntax is and why it exists.
• Examples ordered from most common to least common. For instance, the variables lesson starts with const (the form you’ll reach for most often), moves on to let, and finishes with var — the least common of the three in modern code.
• A table of contents for that page, linking straight to its sections, plus links to the lesson before and after it so you can move through the series start to finish.
• An “old way of doing things” section at the end of most lessons, explaining how JavaScript developers used to solve the same problem and why the language moved on. Knowing the old way helps you read older code and understand why the modern syntax is preferred.

The list below is also the recommended reading order — lessons build on each other, so working through them top to bottom will make each new one easier to follow.

This series intentionally sticks to essentials and syntax. Topics like promises, async/await, and regular expressions are deliberately left out — they deserve their own dedicated series once you’re comfortable with the fundamentals covered here.