Bun Cloudflare Workers

Build and deploy Cloudflare Workers using Bun for development.

Quick Start

# Create new Workers project
bunx create-cloudflare my-worker
cd my-worker

# Install dependencies
bun install

# Development
bun run dev

# Deploy
bun run deploy

Project Setup

package.json

{
  "scripts": {
    "dev": "wrangler dev",
    "deploy": "wrangler deploy",
    "build": "bun build src/index.ts --outdir=dist --target=browser"
  },
  "devDependencies": {
    "@cloudflare/workers-types": "^4.20250906.0",
    "wrangler": "^4.54.0"
  }
}

wrangler.toml

name = "my-worker"
main = "src/index.ts"
compatibility_date = "2024-01-01"

# Use Bun for local dev
[dev]
local_protocol = "http"

# Bindings
[[kv_namespaces]]
binding = "KV"
id = "xxx"

[[d1_databases]]
binding = "DB"
database_name = "my-db"
database_id = "xxx"

Basic Worker

// src/index.ts
export default {
  async fetch(request: Request, env: Env, ctx: ExecutionContext): Promise<Response> {
    const url = new URL(request.url);

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

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

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

interface Env {
  KV: KVNamespace;
  DB: D1Database;
}

Using Hono

// src/index.ts
import { Hono } from "hono";

type Bindings = {
  KV: KVNamespace;
  DB: D1Database;
};

const app = new Hono<{ Bindings: Bindings }>();

app.get("/", (c) => c.text("Hello Hono!"));

app.get("/api/users", async (c) => {
  const users = await c.env.DB.prepare("SELECT * FROM users").all();
  return c.json(users.results);
});

app.post("/api/users", async (c) => {
  const { name } = await c.req.json();
  await c.env.DB.prepare("INSERT INTO users (name) VALUES (?)").bind(name).run();
  return c.json({ success: true });
});

export default app;

KV Storage

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const url = new URL(request.url);
    const key = url.searchParams.get("key");

    if (request.method === "GET" && key) {
      const value = await env.KV.get(key);
      return Response.json({ key, value });
    }

    if (request.method === "PUT" && key) {
      const value = await request.text();
      await env.KV.put(key, value, { expirationTtl: 3600 });
      return Response.json({ success: true });
    }

    return new Response("Bad Request", { status: 400 });
  },
};

D1 Database

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    // Query
    const { results } = await env.DB.prepare(
      "SELECT * FROM users WHERE active = ?"
    ).bind(1).all();

    // Insert
    const info = await env.DB.prepare(
      "INSERT INTO users (name, email) VALUES (?, ?)"
    ).bind("Alice", "alice@example.com").run();

    // Transaction
    const batch = await env.DB.batch([
      env.DB.prepare("INSERT INTO users (name) VALUES (?)").bind("Bob"),
      env.DB.prepare("INSERT INTO users (name) VALUES (?)").bind("Charlie"),
    ]);

    return Response.json(results);
  },
};

Durable Objects

// src/counter.ts
export class Counter {
  private state: DurableObjectState;
  private value = 0;

  constructor(state: DurableObjectState) {
    this.state = state;
    this.state.blockConcurrencyWhile(async () => {
      this.value = (await this.state.storage.get("value")) || 0;
    });
  }

  async fetch(request: Request): Promise<Response> {
    const url = new URL(request.url);

    if (url.pathname === "/increment") {
      this.value++;
      await this.state.storage.put("value", this.value);
    }

    return Response.json({ value: this.value });
  }
}

// src/index.ts
export { Counter } from "./counter";

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const id = env.COUNTER.idFromName("global");
    const stub = env.COUNTER.get(id);
    return stub.fetch(request);
  },
};

# wrangler.toml
[[durable_objects.bindings]]
name = "COUNTER"
class_name = "Counter"

[[migrations]]
tag = "v1"
new_classes = ["Counter"]

R2 Storage

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const url = new URL(request.url);
    const key = url.pathname.slice(1);

    if (request.method === "GET") {
      const object = await env.BUCKET.get(key);
      if (!object) {
        return new Response("Not Found", { status: 404 });
      }
      return new Response(object.body, {
        headers: { "Content-Type": object.httpMetadata?.contentType || "application/octet-stream" },
      });
    }

    if (request.method === "PUT") {
      await env.BUCKET.put(key, request.body, {
        httpMetadata: { contentType: request.headers.get("Content-Type") || undefined },
      });
      return Response.json({ success: true });
    }

    return new Response("Method Not Allowed", { status: 405 });
  },
};

Development with Bun

Local Development

# Run with wrangler (uses Bun for TypeScript)
bun run dev

# Or directly
bunx wrangler dev

Testing with Bun

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

// Mock worker
const worker = {
  async fetch(request: Request) {
    return new Response("Hello");
  },
};

describe("Worker", () => {
  test("returns hello", async () => {
    const request = new Request("http://localhost/");
    const response = await worker.fetch(request);
    expect(await response.text()).toBe("Hello");
  });
});

Miniflare for Testing

import { Miniflare } from "miniflare";

const mf = new Miniflare({
  script: await Bun.file("./dist/index.js").text(),
  kvNamespaces: ["KV"],
});

const response = await mf.dispatchFetch("http://localhost/");
console.log(await response.text());

Build for Production

// build.ts
await Bun.build({
  entrypoints: ["./src/index.ts"],
  outdir: "./dist",
  target: "browser", // Workers use browser APIs
  minify: true,
  sourcemap: "external",
});

bun run build.ts
bunx wrangler deploy

Environment Variables

# wrangler.toml
[vars]
API_URL = "https://api.example.com"

# Secrets (set via CLI)
# wrangler secret put API_KEY

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    console.log(env.API_URL);    // From vars
    console.log(env.API_KEY);    // From secrets
    return new Response("OK");
  },
};

Scheduled Workers (Cron)

export default {
  async scheduled(event: ScheduledEvent, env: Env, ctx: ExecutionContext): Promise<void> {
    console.log("Cron triggered at:", event.scheduledTime);
    // Perform scheduled task
    await env.DB.prepare("DELETE FROM logs WHERE created_at < ?")
      .bind(Date.now() - 7 * 24 * 60 * 60 * 1000)
      .run();
  },

  async fetch(request: Request, env: Env): Promise<Response> {
    return new Response("OK");
  },
};

# wrangler.toml
[triggers]
crons = ["0 * * * *"]  # Every hour

Common Errors

Error	Cause	Fix
Bun API not available	Workers use V8	Use Web APIs only
Module not found	Build issue	Check bundler config
Script too large	Exceeds 10MB	Optimize bundle
CPU time exceeded	Long execution	Optimize or use queues

API Compatibility

Workers support Web APIs, NOT Bun-specific APIs:

Available	Not Available
fetch()	Bun.file()
Response	Bun.serve()
Request	bun:sqlite
URL	bun:ffi
crypto	fs
TextEncoder	child_process

When to Load References

Load references/bindings.md when:

• Advanced KV/D1/R2 patterns
• Queue workers
• Service bindings

Load references/performance.md when:

• Bundle optimization
• Cold start reduction
• Caching strategies