Does TypeScript run in the browser?

Browsers run JavaScript, not TypeScript. The compiler (or a build tool) converts your TypeScript to JavaScript first.

Do I have to rewrite my JavaScript to use TypeScript?

No. TypeScript is a superset of JavaScript, so valid JavaScript is valid TypeScript. You can adopt types gradually, file by file.

TypeScript for Beginners: Setup and Your First Types

Introduction

TypeScript is JavaScript with static types. You write TypeScript, the compiler checks it for mistakes, and it outputs plain JavaScript that runs anywhere JavaScript does. This tutorial gets you set up and shows the compiler catching a real error.

Prerequisites

Node.js 18 or newer installed
Basic JavaScript knowledge

Step-by-Step Guide

Step 1: Create a project and install TypeScript

Install the compiler as a development dependency in a new project.

mkdir ts-demo
cd ts-demo
npm init -y
npm install --save-dev typescript

Step 2: Generate a tsconfig.json

The tsconfig.json file tells the compiler how to check and emit your code. The init command creates one with sensible defaults and comments explaining each option.

npx tsc --init

Step 3: Write typed code

Create hello.ts. Annotate parameters and return values with types after a colon.

function greet(name: string): string {
  return "Hello, " + name;
}

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

Step 4: Compile and run

tsc compiles hello.ts into hello.js, which you run with Node. To run TypeScript directly while experimenting, you can also use npx tsx hello.ts.

npx tsc
node hello.js

Step 5: See the compiler catch a mistake

Passing the wrong type is now an error at compile time, not a surprise at runtime.

greet(42);
// Error: Argument of type 'number' is not assignable to parameter of type 'string'.

FAQs

Does TypeScript run in the browser?: Browsers run JavaScript, not TypeScript. The compiler (or a build tool) converts your TypeScript to JavaScript first.
Do I have to rewrite my JavaScript to use TypeScript?: No. TypeScript is a superset of JavaScript, so valid JavaScript is valid TypeScript. You can adopt types gradually, file by file.

Summary

Install typescript, run tsc --init, add types to your code, and compile. The payoff is that many bugs surface in your editor and build instead of in production.