Bun JS Quickstart

Overview

Build a minimal HTTP server with Bun.serve, run it locally, then evolve it by installing a package.

::: Prerequisites: Bun installed and available on your PATH. See installation for setup. :::

Initialize a new project with bun init.

bash

bun init my-app

It'll prompt you to pick a template, either Blank, React, or Library. For this guide, we'll pick Blank.

bash

bun init my-app

bash

✓ Select a project template: Blank

- .gitignore
- CLAUDE.md
- .cursor/rules/use-bun-instead-of-node-vite-npm-pnpm.mdc -> CLAUDE.md
- index.ts
- tsconfig.json (for editor autocomplete)
- README.md

This automatically creates a my-app directory with a basic Bun app.

Run the index.ts file using bun run index.ts.

bash

cd my-app
bun run index.ts

bash

Hello via Bun!

You should see a console output saying "Hello via Bun!".

Replace the contents of index.ts with the following code:

const server = Bun.serve({
  port: 3000,
  routes: {
    "/": () => new Response('Bun!'),
  }
});

console.log(`Listening on ${server.url}`);

Run the index.ts file again using bun run index.ts.

bash

bun run index.ts

bash

Listening on http://localhost:3000

Visit http://localhost:3000 to test the server. You should see a simple page that says "Bun!".

Seeing TypeScript errors on Bun?

If you used bun init, Bun will have automatically installed Bun's TypeScript declarations and configured your tsconfig.json. If you're trying out Bun in an existing project, you may see a type error on the Bun global.

To fix this, first install @types/bun as a dev dependency.

bash

bun add -d @types/bun

Then add the following to your compilerOptions in tsconfig.json:

json

{
  "compilerOptions": {
    "lib": ["ESNext"],
    "target": "ESNext",
    "module": "Preserve",
    "moduleDetection": "force",
    "moduleResolution": "bundler",
    "allowImportingTsExtensions": true,
    "verbatimModuleSyntax": true,
    "noEmit": true
  }
}

Install the figlet package and its type declarations. Figlet is a utility for converting strings into ASCII art.

bash

bun add figlet
bun add -d @types/figlet # TypeScript users only

Update index.ts to use figlet in routes.

import figlet from 'figlet';

const server = Bun.serve({
  port: 3000,
  routes: {
    "/": () => new Response('Bun!'),
    "/figlet": () => {
      const body = figlet.textSync('Bun!');
      return new Response(body);
    } 
  }
});

Run the index.ts file again using bun run index.ts.

bash

bun run index.ts

bash

Listening on http://localhost:3000

Visit http://localhost:3000/figlet to test the server. You should see a simple page that says "Bun!" in ASCII art.

bash

____              _
| __ ) _   _ _ __ | |
|  _ \| | | | '_ \| |
| |_) | |_| | | | |_|
|____/ \__,_|_| |_(_)

Let's add some HTML. Create a new file called index.html and add the following code:

html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Bun</title>
  </head>
  <body>
    <h1>Bun!</h1>
  </body>
</html>

Then, import this file in index.ts and serve it from the root / route.

import figlet from 'figlet';
import index from './index.html'; 

const server = Bun.serve({
  port: 3000,
  routes: {
    "/": index, 
    "/figlet": () => {
      const body = figlet.textSync('Bun!');
      return new Response(body);
    }
  }
});

console.log(Listening on ${server.url});

Run the index.ts file again using bun run index.ts.

bash

bun run index.ts

txt

Listening on http://localhost:3000

Visit http://localhost:3000 to test the server. You should see the static HTML page.

🎉 Congratulations! You've built a simple HTTP server with Bun and installed a package.

Run a script

Bun can also execute "scripts" from your package.json. Add the following script:

json

{
  "name": "quickstart",
  "module": "index.ts",
  "type": "module",
  "private": true,
  "scripts": { 
    "start": "bun run index.ts"
  }, 
  "devDependencies": {
    "@types/bun": "latest"
  },
  "peerDependencies": {
    "typescript": "^5"
  }
}

Then run it with bun run start.

bash

bun run start

bash

Listening on http://localhost:3000

INFO

Performance — bun run is roughly 28x faster than npm run (6ms vs 170ms of overhead).

Overview ​

Seeing TypeScript errors on Bun? ​

Run a script ​

Overview

Seeing TypeScript errors on Bun?

Run a script