vercel-bun

Bun runtime for Vercel serverless functions

Important

Bun is now an officially supported runtime on Vercel, so I do NOT recommend using this custom Bun runtime unless:

1. You have critical, unsolvable issues with the official runtime
2. You want to run your serverless functions with a specific version of Bun

Please reference the Vercel documentation here for more information: https://vercel.com/docs/functions/runtimes/bun

Overview

vercel-bun is a custom Vercel runtime that enables you to run serverless functions using the Bun JavaScript runtime instead of Node.js. This runtime provides improved performance, better TypeScript support, and access to Bun's native APIs.

Features

• 🚀 High Performance: Uses Bun's fast JavaScript runtime (version 1.2.15 by default)
• 📦 Native TypeScript: Built-in TypeScript support without additional compilation
• 🌐 Web Standard APIs: Uses native Request and Response interfaces
• 🏗️ Framework Agnostic: Works with any framework that supports Bun (Elysia, Hono, etc.)
• 🔧 Configurable: Customizable Bun version

Usage

1. Configure your vercel.json file

{
  "$schema": "https://openapi.vercel.sh/vercel.json",
  "functions": {
    "api/index.ts": {
      "runtime": "@godsreveal/[email protected]"
    }
  },
  // Optional: use if you want all /api routes to be handled by /api/index.ts
  "rewrites": [{ "source": "/api/(.*)", "destination": "/api/index.ts" }]
}

2. Create a Bun serverless function

Basic Handler (Vanilla)

// api/index.ts
export default function handler(req: Request) {
  return new Response(
    JSON.stringify({ message: `Hello from bun@${Bun.version}` }),
    {
      headers: { "Content-Type": "application/json" },
    }
  );
}

Advanced Handler (with Elysia)

// api/index.ts
import { Elysia, t } from "elysia";

const app = new Elysia({ prefix: "/api" })
  .get("/", () => `Hello from bun@${Bun.version}`)
  .get("/hello", ({ query }) => `Hello ${query.firstName} ${query.lastName}`, {
    query: t.Object({
      firstName: t.String(),
      lastName: t.String(),
    }),
  })
  .post(
    "/users",
    async ({ body }) => {
      // Your logic here
      return { success: true, data: body };
    },
    {
      body: t.Object({
        name: t.String(),
        email: t.String(),
      }),
    }
  );

// Development server (runs locally with `bun run api/index.ts`)
if (process.env.NODE_ENV !== "production") {
  app.listen({ port: 3000 });
  console.log("Server is running on http://localhost:3000");
}

export default app.handle;

3. Deploy to Vercel

Deploy your GitHub repository to Vercel.

Configuration

Environment Variables

| Variable | Description | Default | Example | | ------------- | ------------------------------ | -------- | -------- | | BUN_VERSION | Specify the Bun version to use | 1.2.15 | 1.2.15 |

Examples

See the examples directory for several examples:

• Vanilla - A comprehensive benchmarking suite comparing Bun and Node.js runtime performance on Vercel serverless functions, including cold start, throughput, concurrency, and payload size tests.

• Next.js + ElysiaJS - A full-stack Next.js application demonstrating high-performance serverless functions with Elysia REST API, Redis integration, Cloudflare R2 image uploads, and end-to-end type safety using Eden Treaty.

• Next.js + Hono - A lightweight and fast Next.js application showcasing serverless functions with the Hono web framework, featuring type-safe request validation with Zod and optimized performance for edge computing.

• grammY - A Telegram bot built with the grammY framework, showcasing how to deploy chatbots as serverless functions using the Bun runtime with webhook support and modular command structure.

Goals

• [ ] First-class Vercel Integration: Native Bun runtime support in Vercel's platform for both serverless and edge functions.
• [ ] Next.js Integration: Runtime specification in next.config.js for API routes and React Server Components.