Node to Bun Guide

🧭 Node to Bun Guide: The Modern Switch

If you've been building with Node.js and you're curious about Bun — the lightning-fast, all-in-one JavaScript runtime — you're in for a treat 🚀. This guide will walk you through everything you need to know to switch from Node to Bun smoothly, including differences, migration strategies, and practical examples.

⚙️ What is Bun and Why Should You Care?

Bun is a modern JavaScript runtime like Node.js, but it also includes a native bundler, test runner, transpiler, and even its own package manager — all written in Zig for ultimate speed ⚡.

• 💨 Faster than Node in most benchmarks
• 📦 Built-in package manager (bun install)
• 🧪 Zero-config test runner (bun test)
• 🔧 Native support for TypeScript, JSX

📁 Migrating a Basic Node App to Bun

Let’s say you have a basic Node.js server using Express. Here’s what that might look like:

// Node.js (server.js)
const express = require("express");
const app = express();

app.get("/", (req, res) => {
  res.send("Hello from Node");
});

app.listen(3000, () => console.log("Server running"));

To convert this to Bun, you don't even need Express. Here's the Bun-native version:

// Bun (index.ts)
Bun.serve({
  port: 3000,
  fetch(req) {
    return new Response("👋 Hello from Bun!");
  }
});

No third-party libraries needed. You’ve now got a server with just a few lines of code — and it’s blazing fast 🔥.

📦 Switching Package Manager: npm to bun install

In Node.js, you probably use npm install or yarn. In Bun, just run:

bun install

It reads your package.json and installs dependencies way faster — no need for node_modules bloat. You can also use bun add, bun remove, and more.

🧪 Replacing Jest or Mocha with bun test

Bun has a built-in test runner. No setup, no config files, no dependencies.

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

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

Just run:

bun test

Done. You're testing in seconds 🧪✅.

🛠 Common Node Modules in Bun

Bun provides built-in polyfills for many Node modules:

• fs ✅
• path ✅
• buffer ✅
• crypto ✅

Most packages that work with Node also work in Bun, especially if they’re ESM-friendly. Bun supports both ESM and CommonJS, but ESM is preferred 🌍.

📚 Example: Using a Database

In Node, you might use something like mysql2. In Bun, it's the same package — just faster installs and native performance:

import mysql from "mysql2/promise";

const conn = await mysql.createConnection({
  host: "localhost",
  user: "root",
  database: "bun_db"
});

const [rows] = await conn.query("SELECT * FROM users");
console.log(rows);

🧩 Bun Build: Bundling & Transpiling

Instead of using Webpack, Parcel, or Vite, Bun can bundle and transpile TypeScript, JSX, and more out of the box:

bun build src/index.ts --outdir=dist --minify

Perfect for frontend builds or small libraries 🔧.

🎯 Migrating Real Projects: Tips

• ✅ Start by replacing node with bun in scripts
• ✅ Replace npm install with bun install
• ✅ Test your API routes using Bun’s native server
• ✅ Use bun test instead of Jest or Mocha

Keep your migration modular. Move one piece at a time, especially when working with large Node apps 🛠️.

🌐 Frameworks That Support Bun

Bun is gaining framework support rapidly:

• 🧱 Elysia.js
• 📡 Hono (via compatibility mode)
• 🌲 Next.js (limited via custom server)
• 🔋 React, Vue, Svelte — frontend bundling is lightning fast

📌 Summary: Node to Bun in a Nutshell

Migrating from Node.js to Bun brings you:

• 🚀 Speed in development and runtime
• 📦 Unified tooling (runtime + bundler + test runner)
• 🧠 Simpler project management
• 📉 Fewer dependencies and configs