Getting Started

Your first program

Create src/index.ts:

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

const message = greet("TypeScript");
console.log(message);

The : string parts are type annotations. Call greet(42) and the compiler rejects it before the code ever runs. Because the config uses "module": "nodenext", also add "type": "module" to package.json so Node treats the emitted files as ES modules. Then build and run:

npx tsc
node dist/index.js

tsc checks everything under src and writes dist/index.js. One surprise for newcomers: by default it still emits JavaScript even when there are type errors. If you would rather block output on errors, enable noEmitOnError.

Running TypeScript without a build step

Compiling before every run gets tedious during development. tsx executes .ts files directly by stripping the types on the fly. It does not type-check, though, so pair it with tsc --noEmit, which checks without writing any files.

npm install --save-dev tsx
npx tsx src/index.ts
npx tsx watch src/index.ts
npx tsc --noEmit

Recent Node.js releases can also run .ts files natively by erasing type annotations. Syntax that needs real code generation, such as enum, has limited support there, so check the documentation for the Node.js version you use before relying on it.

Wire the common commands into package.json so nobody has to remember them:

{
  "type": "module",
  "scripts": {
    "dev": "tsx watch src/index.ts",
    "build": "tsc",
    "typecheck": "tsc --noEmit",
    "start": "node dist/index.js"
  }
}

Editor setup

Visual Studio Code bundles the TypeScript language service, so completions, inline errors, rename, and go-to-definition work out of the box. A few habits make it even better:

• Run TypeScript: Select TypeScript Version from the command palette and pick "Use Workspace Version", so the editor and npx tsc agree.
• Hover over any variable to see its inferred type. This is the first thing to check when the compiler disagrees with you.
• Long error messages read best from the bottom up; the last line usually names the real mismatch.
• Add ESLint and Prettier to catch common mistakes and keep formatting consistent.

JetBrains IDEs such as WebStorm support TypeScript out of the box as well. To experiment without installing anything, open the TypeScript Playground in your browser.

Summary

• TypeScript is type-checked and compiled to JavaScript; types disappear at runtime.
• Install it per project with npm install --save-dev typescript and run it via npx tsc.
• Enable strict in tsconfig.json from the start.
• Use tsc for builds, tsx for quick runs during development, and tsc --noEmit for type checking.