Native Modules in Bun

📦 What Are Native Modules in Bun?

In Bun, native modules refer to precompiled code (usually written in C, C++, or Rust) that can be imported directly into your Bun app. These modules unlock near-native performance, giving you the ability to execute high-performance logic inside your JavaScript or TypeScript code without external dependencies.

⚙️ Why Use Native Modules?

Sometimes JavaScript just isn’t fast enough — especially for CPU-heavy tasks like encryption, compression, media processing, or complex algorithms. Bun’s support for native modules means:

• Lower-level access to system APIs
• Significant performance boosts
• Shared logic between JS and native codebases

Think of it like turbocharging your app — native modules handle the heavy lifting while Bun handles orchestration.

🔌 Loading Native Modules in Bun

You can load native code into your Bun project using the ffi module. Here’s a quick breakdown of how it works.

🧪 Example: Loading a Native .so/.dll/.dylib File

Let’s assume you have a compiled shared library named libmath.so (Linux), math.dylib (macOS), or math.dll (Windows). You can load it like this:

const lib = new FFI({
  name: "math",
  path: "./libmath.so", // or .dylib/.dll
  exports: {
    add: {
      args: ["int", "int"],
      returns: "int"
    }
  }
});

console.log("2 + 3 =", lib.symbols.add(2, 3));

This calls the native add function defined in your compiled C/C++ code — all from within your Bun app.

🛠️ Building Native Modules

To use native functions, you’ll first need to write and compile your native code. Here's an example in C:

// math.c
int add(int a, int b) {
  return a + b;
}

Then compile it as a shared library:

# Linux
gcc -shared -o libmath.so -fPIC math.c

# macOS
gcc -shared -o libmath.dylib -fPIC math.c

# Windows
gcc -shared -o math.dll math.c

🔒 Safety & Stability Tips

When dealing with native modules, crashes in native code can crash your Bun app. To reduce risk:

• Validate input before sending to native code
• Use safe memory operations and error handling
• Test extensively across all supported platforms

📚 Data Type Mapping in FFI

Bun's FFI supports several data types for interop:

• int, float, double for numbers
• ptr for memory addresses
• cstring for null-terminated strings

exports: {
  greet: {
    args: ["cstring"],
    returns: "void"
  }
}

Use this mapping carefully to prevent memory corruption or crashes.

💡 When Should You Use Native Modules?

Native modules are powerful, but not always necessary. Use them when:

• Performance is a critical bottleneck
• You’re working with legacy native libraries
• You need to access OS-level APIs not exposed by Bun/JS

For most web apps, Bun’s JavaScript engine is fast enough. Native modules shine in specialized use cases.

🚧 Future of Native Modules in Bun

Bun's native module ecosystem is still evolving. Expect improvements like:

• WASM + native hybrid execution
• More ergonomic FFI syntax
• Prebuilt binary support via Bun packages

As the ecosystem matures, writing high-performance Bun apps with native integrations will only get easier.

✅ Conclusion: Level Up with Native Power

Native modules in Bun bridge the gap between lightning-fast native code and the modern JS ecosystem. Whether you're optimizing for speed or integrating legacy systems, this feature gives you the best of both worlds — native power with JavaScript simplicity.

Start experimenting, test your performance, and explore new levels of optimization inside your Bun apps.