Introduction to TypeScript

TypeScript is JavaScript with static types — the same language you already run in the browser, plus a compiler that catches mistakes before they ship.

¶What is TypeScript?

TypeScript is a superset of JavaScript: every valid JavaScript program is already valid TypeScript.

You add type annotations, and the TypeScript compiler checks them and then erases them, emitting plain JavaScript that runs anywhere.

¶Your first example

Here is TypeScript saying hello. Read it top to bottom — every line earns its place.

function greet(name: string): string {
  return `Hello, ${name}!`;
}

console.log(greet("world"));

Hello, world!

¶Why learn TypeScript?

• Catch typos, null bugs, and bad refactors at compile time instead of in production.
• Editor autocomplete and "go to definition" become reliable across an entire codebase.
• It is the default for serious frontend and Node work — React, Next.js, Angular, and most libraries ship types.

¶Where it is used

• Large web apps
• Node.js services
• Open-source libraries
• Anywhere JavaScript runs

¶How this track works

Every topic here has four views, switchable with the tabs at the top of each page:

• Learn — the clear, practical walkthrough you are reading now.
• Deep — every detail: edge cases, the full API, and what is really happening.
• Reference — a scannable, no-fluff lookup for when you already know the shape.
• Cheatsheet — the one-page summary, printable, for quick recall.