Bun

TL;DR

What: All-in-one JavaScript runtime, bundler, test runner, and package manager.

Why: 4x faster than Node.js, native TypeScript, built-in bundler, drop-in Node replacement.

Quick Start

Install:

# macOS/Linux
curl -fsSL https://bun.sh/install | bash

# Windows
powershell -c "irm bun.sh/install.ps1 | iex"

# Check version
bun --version

Run scripts:

bun run index.ts     # Run TypeScript directly
bun run index.js     # Run JavaScript
bun run dev          # Run package.json script

Cheatsheet

Command	Description
bun run file	Run file
bun install	Install dependencies
bun add pkg	Add dependency
bun remove pkg	Remove package
bun test	Run tests
bun build	Bundle for production
bun init	Create new project

Gotchas

Package management

# Initialize project
bun init

# Install dependencies
bun install

# Add package
bun add express

# Add dev dependency
bun add -d typescript

# Remove package
bun remove lodash

# Update packages
bun update

Running scripts

# Run TypeScript directly
bun run app.ts

# Run with watch mode
bun --watch run app.ts

# Run package.json script
bun run dev

# Run script (shorthand)
bun dev

HTTP server

// server.ts
const server = Bun.serve({
  port: 3000,
  fetch(request) {
    const url = new URL(request.url);

    if (url.pathname === "/") {
      return new Response("Hello Bun!");
    }

    if (url.pathname === "/json") {
      return Response.json({ message: "Hello" });
    }

    return new Response("Not Found", { status: 404 });
  },
});

console.log(`Listening on http://localhost:${server.port}`);

File I/O

// Read file
const file = Bun.file("./data.json");
const text = await file.text();
const json = await file.json();

// Write file
await Bun.write("./output.txt", "Hello World");
await Bun.write("./data.json", JSON.stringify({ key: "value" }));

// Check if exists
const exists = await Bun.file("./data.json").exists();

Testing

// math.test.ts
import { describe, expect, test } from "bun:test";

describe("math", () => {
  test("2 + 2", () => {
    expect(2 + 2).toBe(4);
  });

  test("async test", async () => {
    const result = await Promise.resolve(42);
    expect(result).toBe(42);
  });
});

bun test
bun test --watch

Bundler

# Bundle for browser
bun build ./src/index.ts --outdir ./dist

# With minification
bun build ./src/index.ts --outdir ./dist --minify

# For Node.js
bun build ./src/index.ts --outdir ./dist --target node

// Programmatic bundling
const result = await Bun.build({
  entrypoints: ['./src/index.ts'],
  outdir: './dist',
  minify: true,
  splitting: true,
});

Next Steps

• Bun Documentation - Official docs
• Bun APIs - Built-in APIs
• Bun Discord - Community
• Bun GitHub - Source code