Bun and External Modules

🔌 Bun and External Modules: Smooth Integrations Made Easy

One of the most crucial aspects of any JavaScript runtime is how well it handles third-party packages. With the rising popularity of Bun, developers often wonder — how does it deal with external modules? In this blog, we'll break down everything you need to know about working with Bun and External Modules, from installation to compatibility with npm packages.

📦 What Are External Modules?

External modules refer to third-party libraries or packages that aren't a part of your native JavaScript or Bun codebase. These include popular packages like lodash, axios, express, and thousands more from the npm registry.

Traditionally, developers use npm or yarn to install and manage these modules. But with Bun, the process is much faster and streamlined.

⚡ Installing External Packages with Bun

Bun replaces npm install with its own blazing-fast bun install. It fetches packages from the npm registry by default and handles linking in milliseconds.

bun install axios

This command will:

• Download the axios package
• Install it into the project
• Link it properly into your node_modules folder

📁 Where Are the Modules Stored?

Although Bun tries to virtualize its modules and make installation faster, it still respects the familiar node_modules structure. It also generates a bun.lockb file to lock dependency versions.

my-project/
├── node_modules/
├── bun.lockb
├── package.json

🔧 Importing Modules in Bun

Bun supports both CommonJS (require) and ES Modules (import) syntax. You can choose based on your use case or package structure.

// ES Module syntax
import axios from "axios";

axios.get("https://api.example.com").then(res => {
  console.log(res.data);
});

// CommonJS syntax
const lodash = require("lodash");
console.log(lodash.capitalize("bun rocks"));

**Bun detects the type automatically**, no need to manually set the module system in most cases.

🔄 Compatibility with npm Modules

One of Bun’s top priorities is npm compatibility. While it's not 100% yet, most popular packages work out of the box. Bun mimics Node.js behavior closely, so you can expect seamless usage for most libraries.

Here are a few external libraries that work perfectly with Bun:

• axios
• dotenv
• chalk
• lodash
• zod

🧪 Testing External Modules

Bun has a built-in test runner that allows you to test functionality involving external modules without any extra setup.

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

test("GET request", async () => {
  const response = await axios.get("https://jsonplaceholder.typicode.com/posts/1");
  expect(response.data.id).toBe(1);
});

🧠 Handling Peer Dependencies

Bun currently installs peer dependencies automatically — something npm doesn’t always do. This makes it easier to work with packages that depend on other libraries like react or webpack.

bun install react react-dom

No additional manual peer installs needed — Bun handles it for you.

📌 Things to Watch Out For

Although Bun is fast and modern, it’s still catching up in some areas:

• Some advanced Node.js APIs (like fs.promises) may not be fully supported
• Native modules or those with C++ bindings might fail
• Older packages with strict CommonJS assumptions may require tweaks

However, the team is rapidly improving compatibility and community support is growing quickly.

✅ Final Thoughts

Working with Bun and External Modules is refreshingly simple and fast. Whether you're installing lightweight utility libraries or complex frameworks, Bun handles it with speed and elegance. If you're tired of waiting around for installs and want a next-gen JavaScript experience, Bun is absolutely worth trying.

🚀 Pro Tip: Combine Bun + ESBuild

For even faster builds with external modules, leverage Bun’s built-in bundler (powered by ESBuild). You get a bundled, optimized output ready for production — no extra tools needed.

bun build index.ts --outfile=bundle.js

This will bundle your app and all external modules into one deployable file.