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Build fullstack applications with Bun's integrated dev server that bundles frontend assets and handles API routes
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Hot Module Replacement (HMR) for Bun's development server
| name | Bun Fullstack dev server |
| description | Build fullstack applications with Bun's integrated dev server that bundles frontend assets and handles API routes |
Build fullstack applications with Bun's integrated dev server that bundles frontend assets and handles API routes
To get started, import HTML files and pass them to the routes option in Bun.serve().
import { serve } from "bun";
import dashboard from "./dashboard.html";
import homepage from "./index.html";
const server = serve({
routes: {
// ** HTML imports **
// Bundle & route index.html to "/". This uses HTMLRewriter to scan
// the HTML for `<script>` and `<link>` tags, runs Bun's JavaScript
// & CSS bundler on them, transpiles any TypeScript, JSX, and TSX,
// downlevels CSS with Bun's CSS parser and serves the result.
"/": homepage,
// Bundle & route dashboard.html to "/dashboard"
"/dashboard": dashboard,
// ** API endpoints ** (Bun v1.2.3+ required)
"/api/users": {
async GET(req) {
const users = await sql`SELECT * FROM users`;
return Response.json(users);
},
async POST(req) {
const { name, email } = await req.json();
const [user] = await sql`INSERT INTO users (name, email) VALUES (${name}, ${email})`;
return Response.json(user);
},
},
"/api/users/:id": async req => {
const { id } = req.params;
const [user] = await sql`SELECT * FROM users WHERE id = ${id}`;
return Response.json(user);
},
},
// Enable development mode for:
// - Detailed error messages
// - Hot reloading (Bun v1.2.3+ required)
development: true,
});
console.log(`Listening on ${server.url}`);
bun run app.ts
The web starts with HTML, and so does Bun's fullstack dev server.
To specify entrypoints to your frontend, import HTML files into your JavaScript/TypeScript/TSX/JSX files.
import dashboard from "./dashboard.html";
import homepage from "./index.html";
These HTML files are used as routes in Bun's dev server you can pass to Bun.serve().
Bun.serve({
routes: {
"/": homepage,
"/dashboard": dashboard,
},
fetch(req) {
// ... api requests
},
});
When you make a request to /dashboard or /, Bun automatically bundles the <script> and <link> tags in the HTML files, exposes them as static routes, and serves the result.
An index.html file like this:
<!DOCTYPE html>
<html>
<head>
<title>Home</title>
<link rel="stylesheet" href="./reset.css" />
<link rel="stylesheet" href="./styles.css" />
</head>
<body>
<div id="root"></div>
<script type="module" src="./sentry-and-preloads.ts"></script>
<script type="module" src="./my-app.tsx"></script>
</body>
</html>
Becomes something like this:
<!DOCTYPE html>
<html>
<head>
<title>Home</title>
<link rel="stylesheet" href="/index-[hash].css" />
</head>
<body>
<div id="root"></div>
<script type="module" src="/index-[hash].js"></script>
</body>
</html>
To use React in your client-side code, import react-dom/client and render your app.
serve({ routes: { "/": dashboard, }, async fetch(req) { // ...api requests return new Response("hello world"); }, });
```tsx title="src/frontend.tsx" icon="https://mintcdn.com/bun-1dd33a4e/nIz6GtMH5K-dfXeV/icons/typescript.svg?fit=max&auto=format&n=nIz6GtMH5K-dfXeV&q=85&s=5d73d76daf7eb7b158469d8c30d349b0" theme={"theme":{"light":"github-light","dark":"dracula"}}
import { createRoot } from 'react-dom/client';
import App from './app';
const container = document.getElementById('root');
const root = createRoot(container!);
root.render(<App />);
<!DOCTYPE html>
<html>
<head>
<title>Dashboard</title>
<link rel="stylesheet" href="../src/styles.css" />
</head>
<body>
<div id="root"></div>
<script type="module" src="../src/frontend.tsx"></script>
</body>
</html>
import { useState } from "react";
export default function App() {
const [count, setCount] = useState(0);
return (
<div>
<h1>Dashboard</h1>
<button onClick={() => setCount(count + 1)}>Count: {count}</button>
</div>
);
}
When building locally, enable development mode by setting development: true in Bun.serve().
import homepage from "./index.html";
import dashboard from "./dashboard.html";
Bun.serve({
routes: {
"/": homepage,
"/dashboard": dashboard,
},
development: true,
fetch(req) {
// ... api requests
},
});
When development is true, Bun will:
.html filehmr: false is set)Bun.serve() supports echoing console logs from the browser to the terminal.
To enable this, pass console: true in the development object in Bun.serve().
import homepage from "./index.html";
Bun.serve({
// development can also be an object.
development: {
// Enable Hot Module Reloading
hmr: true,
// Echo console logs from the browser to the terminal
console: true,
},
routes: {
"/": homepage,
},
});
When console: true is set, Bun will stream console logs from the browser to the terminal. This reuses the existing WebSocket connection from HMR to send the logs.
| Feature | Development | Production |
|---|---|---|
| Source maps | ✅ Enabled | ❌ Disabled |
| Minification | ❌ Disabled | ✅ Enabled |
| Hot reloading | ✅ Enabled | ❌ Disabled |
| Asset bundling | 🔄 On each request | 💾 Cached |
| Console logging | 🖥️ Browser → Terminal | ❌ Disabled |
| Error details | 📝 Detailed | 🔒 Minimal |
Hot reloading and development: true helps you iterate quickly, but in production, your server should be as fast as possible and have as few external dependencies as possible.
As of Bun v1.2.17, you can use Bun.build or bun build to bundle your full-stack application ahead of time.
bun build --target=bun --production --outdir=dist ./src/index.ts
When Bun's bundler sees an HTML import from server-side code, it will bundle the referenced JavaScript/TypeScript/TSX/JSX and CSS files into a manifest object that Bun.serve() can use to serve the assets.
import { serve } from "bun";
import index from "./index.html";
serve({
routes: { "/": index },
});
When adding a build step is too complicated, you can set development: false in Bun.serve().
This will:
.html file, and cache the result in memory until the server restarts.Cache-Control headers and ETag headersimport { serve } from "bun";
import homepage from "./index.html";
serve({
routes: {
"/": homepage,
},
// Production mode
development: false,
});
Define API endpoints with HTTP method handlers:
import { serve } from "bun";
serve({
routes: {
"/api/users": {
async GET(req) {
// Handle GET requests
const users = await getUsers();
return Response.json(users);
},
async POST(req) {
// Handle POST requests
const userData = await req.json();
const user = await createUser(userData);
return Response.json(user, { status: 201 });
},
async PUT(req) {
// Handle PUT requests
const userData = await req.json();
const user = await updateUser(userData);
return Response.json(user);
},
async DELETE(req) {
// Handle DELETE requests
await deleteUser(req.params.id);
return new Response(null, { status: 204 });
},
},
},
});
Use URL parameters in your routes:
serve({
routes: {
// Single parameter
"/api/users/:id": async req => {
const { id } = req.params;
const user = await getUserById(id);
return Response.json(user);
},
// Multiple parameters
"/api/users/:userId/posts/:postId": async req => {
const { userId, postId } = req.params;
const post = await getPostByUser(userId, postId);
return Response.json(post);
},
// Wildcard routes
"/api/files/*": async req => {
const filePath = req.params["*"];
const file = await getFile(filePath);
return new Response(file);
},
},
});
serve({
routes: {
"/api/data": {
async POST(req) {
// Parse JSON body
const body = await req.json();
// Access headers
const auth = req.headers.get("Authorization");
// Access URL parameters
const { id } = req.params;
// Access query parameters
const url = new URL(req.url);
const page = url.searchParams.get("page") || "1";
// Return response
return Response.json({
message: "Data processed",
page: parseInt(page),
authenticated: !!auth,
});
},
},
},
});
Bun's bundler plugins are also supported when bundling static routes.
To configure plugins for Bun.serve, add a plugins array in the [serve.static] section of your bunfig.toml.
You can use TailwindCSS by installing and adding the tailwindcss package and bun-plugin-tailwind plugin.
bun add tailwindcss bun-plugin-tailwind
[serve.static]
plugins = ["bun-plugin-tailwind"]
This will allow you to use TailwindCSS utility classes in your HTML and CSS files. All you need to do is import tailwindcss somewhere:
<!doctype html>
<html>
<head>
<!-- [!code ++] -->
<link rel="stylesheet" href="tailwindcss" />
</head>
<!-- the rest of your HTML... -->
</html>
Alternatively, you can import TailwindCSS in your CSS file:
@import "tailwindcss";
.custom-class {
@apply bg-red-500 text-white;
}
<!doctype html>
<html>
<head>
<!-- [!code ++] -->
<link rel="stylesheet" href="./style.css" />
</head>
<!-- the rest of your HTML... -->
</html>
Any JS file or module which exports a valid bundler plugin object (essentially an object with a name and setup field) can be placed inside the plugins array:
[serve.static]
plugins = ["./my-plugin-implementation.ts"]
import type { BunPlugin } from "bun";
const myPlugin: BunPlugin = {
name: "my-custom-plugin",
setup(build) {
// Plugin implementation
build.onLoad({ filter: /\.custom$/ }, async args => {
const text = await Bun.file(args.path).text();
return {
contents: `export default ${JSON.stringify(text)};`,
loader: "js",
};
});
},
};
export default myPlugin;
Bun will lazily resolve and load each plugin and use them to bundle your routes.
This is currently in `bunfig.toml` to make it possible to know statically which plugins are in use when we eventually integrate this with the `bun build` CLI. These plugins work in `Bun.build()`'s JS API, but are not yet supported in the CLI.Bun can replace process.env.* references in your frontend JavaScript and TypeScript with their actual values at build time. Configure the env option in your bunfig.toml:
[serve.static]
env = "PUBLIC_*" # only inline env vars starting with PUBLIC_ (recommended)
# env = "inline" # inline all environment variables
# env = "disable" # disable env var replacement (default)
If an environment variable is not set, you may see runtime errors like ReferenceError: process is not defined in the browser.
See the HTML & static sites documentation for more details on build-time configuration and examples.
Bun uses HTMLRewriter to scan for <script> and <link> tags in HTML files, uses them as entrypoints for Bun's bundler, generates an optimized bundle for the JavaScript/TypeScript/TSX/JSX and CSS files, and serves the result.
```html title="index.html" icon="file-code" theme={"theme":{"light":"github-light","dark":"dracula"}}
<link rel="stylesheet" href="./styles.css" />
```
Here's a complete fullstack application example:
import { serve } from "bun";
import { Database } from "bun:sqlite";
import homepage from "./public/index.html";
import dashboard from "./public/dashboard.html";
// Initialize database
const db = new Database("app.db");
db.exec(`
CREATE TABLE IF NOT EXISTS users (
id INTEGER PRIMARY KEY AUTOINCREMENT,
name TEXT NOT NULL,
email TEXT UNIQUE NOT NULL,
created_at DATETIME DEFAULT CURRENT_TIMESTAMP
)
`);
const server = serve({
routes: {
// Frontend routes
"/": homepage,
"/dashboard": dashboard,
// API routes
"/api/users": {
async GET() {
const users = db.query("SELECT * FROM users").all();
return Response.json(users);
},
async POST(req) {
const { name, email } = await req.json();
try {
const result = db.query("INSERT INTO users (name, email) VALUES (?, ?) RETURNING *").get(name, email);
return Response.json(result, { status: 201 });
} catch (error) {
return Response.json({ error: "Email already exists" }, { status: 400 });
}
},
},
"/api/users/:id": {
async GET(req) {
const { id } = req.params;
const user = db.query("SELECT * FROM users WHERE id = ?").get(id);
if (!user) {
return Response.json({ error: "User not found" }, { status: 404 });
}
return Response.json(user);
},
async DELETE(req) {
const { id } = req.params;
const result = db.query("DELETE FROM users WHERE id = ?").run(id);
if (result.changes === 0) {
return Response.json({ error: "User not found" }, { status: 404 });
}
return new Response(null, { status: 204 });
},
},
// Health check endpoint
"/api/health": {
GET() {
return Response.json({
status: "ok",
timestamp: new Date().toISOString(),
});
},
},
},
// Enable development mode
development: {
hmr: true,
console: true,
},
// Fallback for unmatched routes
fetch(req) {
return new Response("Not Found", { status: 404 });
},
});
console.log(`🚀 Server running on ${server.url}`);
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<title>Fullstack Bun App</title>
<link rel="stylesheet" href="../src/styles.css" />
</head>
<body>
<div id="root"></div>
<script type="module" src="../src/main.tsx"></script>
</body>
</html>
import { createRoot } from "react-dom/client";
import { App } from "./App";
const container = document.getElementById("root")!;
const root = createRoot(container);
root.render(<App />);
import { useState, useEffect } from "react";
interface User {
id: number;
name: string;
email: string;
created_at: string;
}
export function App() {
const [users, setUsers] = useState<User[]>([]);
const [name, setName] = useState("");
const [email, setEmail] = useState("");
const [loading, setLoading] = useState(false);
const fetchUsers = async () => {
const response = await fetch("/api/users");
const data = await response.json();
setUsers(data);
};
const createUser = async (e: React.FormEvent) => {
e.preventDefault();
setLoading(true);
try {
const response = await fetch("/api/users", {
method: "POST",
headers: { "Content-Type": "application/json" },
body: JSON.stringify({ name, email }),
});
if (response.ok) {
setName("");
setEmail("");
await fetchUsers();
} else {
const error = await response.json();
alert(error.error);
}
} catch (error) {
alert("Failed to create user");
} finally {
setLoading(false);
}
};
const deleteUser = async (id: number) => {
if (!confirm("Are you sure?")) return;
try {
const response = await fetch(`/api/users/${id}`, {
method: "DELETE",
});
if (response.ok) {
await fetchUsers();
}
} catch (error) {
alert("Failed to delete user");
}
};
useEffect(() => {
fetchUsers();
}, []);
return (
<div className="container">
<h1>User Management</h1>
<form onSubmit={createUser} className="form">
<input type="text" placeholder="Name" value={name} onChange={e => setName(e.target.value)} required />
<input type="email" placeholder="Email" value={email} onChange={e => setEmail(e.target.value)} required />
<button type="submit" disabled={loading}>
{loading ? "Creating..." : "Create User"}
</button>
</form>
<div className="users">
<h2>Users ({users.length})</h2>
{users.map(user => (
<div key={user.id} className="user-card">
<div>
<strong>{user.name}</strong>
<br />
<span>{user.email}</span>
</div>
<button onClick={() => deleteUser(user.id)} className="delete-btn">
Delete
</button>
</div>
))}
</div>
</div>
);
}
* {
margin: 0;
padding: 0;
box-sizing: border-box;
}
body {
font-family: -apple-system, BlinkMacSystemFont, sans-serif;
background: #f5f5f5;
color: #333;
}
.container {
max-width: 800px;
margin: 0 auto;
padding: 2rem;
}
h1 {
color: #2563eb;
margin-bottom: 2rem;
}
.form {
background: white;
padding: 1.5rem;
border-radius: 8px;
box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
margin-bottom: 2rem;
display: flex;
gap: 1rem;
flex-wrap: wrap;
}
.form input {
flex: 1;
min-width: 200px;
padding: 0.75rem;
border: 1px solid #ddd;
border-radius: 4px;
}
.form button {
padding: 0.75rem 1.5rem;
background: #2563eb;
color: white;
border: none;
border-radius: 4px;
cursor: pointer;
}
.form button:hover {
background: #1d4ed8;
}
.form button:disabled {
opacity: 0.5;
cursor: not-allowed;
}
.users {
background: white;
padding: 1.5rem;
border-radius: 8px;
box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}
.user-card {
display: flex;
justify-content: space-between;
align-items: center;
padding: 1rem;
border-bottom: 1px solid #eee;
}
.user-card:last-child {
border-bottom: none;
}
.delete-btn {
padding: 0.5rem 1rem;
background: #dc2626;
color: white;
border: none;
border-radius: 4px;
cursor: pointer;
}
.delete-btn:hover {
background: #b91c1c;
}
my-app/
├── src/
│ ├── components/
│ │ ├── Header.tsx
│ │ └── UserList.tsx
│ ├── styles/
│ │ ├── globals.css
│ │ └── components.css
│ ├── utils/
│ │ └── api.ts
│ ├── App.tsx
│ └── main.tsx
├── public/
│ ├── index.html
│ ├── dashboard.html
│ └── favicon.ico
├── server/
│ ├── routes/
│ │ ├── users.ts
│ │ └── auth.ts
│ ├── db/
│ │ └── schema.sql
│ └── index.ts
├── bunfig.toml
└── package.json
export const config = {
development: process.env.NODE_ENV !== "production",
port: process.env.PORT || 3000,
database: {
url: process.env.DATABASE_URL || "./dev.db",
},
cors: {
origin: process.env.CORS_ORIGIN || "*",
},
};
export function errorHandler(error: Error, req: Request) {
console.error("Server error:", error);
if (process.env.NODE_ENV === "production") {
return Response.json({ error: "Internal server error" }, { status: 500 });
}
return Response.json(
{
error: error.message,
stack: error.stack,
},
{ status: 500 },
);
}
export function json(data: any, status = 200) {
return Response.json(data, { status });
}
export function error(message: string, status = 400) {
return Response.json({ error: message }, { status });
}
export function notFound(message = "Not found") {
return error(message, 404);
}
export function unauthorized(message = "Unauthorized") {
return error(message, 401);
}
export interface User {
id: number;
name: string;
email: string;
created_at: string;
}
export interface CreateUserRequest {
name: string;
email: string;
}
export interface ApiResponse<T> {
data?: T;
error?: string;
}
# Build for production
bun build --target=bun --production --outdir=dist ./server/index.ts
# Run production server
NODE_ENV=production bun dist/index.js
FROM oven/bun:1 as base
WORKDIR /usr/src/app
# Install dependencies
COPY package.json bun.lockb ./
RUN bun install --frozen-lockfile
# Copy source code
COPY . .
# Build application
RUN bun build --target=bun --production --outdir=dist ./server/index.ts
# Production stage
FROM oven/bun:1-slim
WORKDIR /usr/src/app
COPY --from=base /usr/src/app/dist ./
COPY --from=base /usr/src/app/public ./public
EXPOSE 3000
CMD ["bun", "index.js"]
NODE_ENV=production
PORT=3000
DATABASE_URL=postgresql://user:pass@localhost:5432/myapp
CORS_ORIGIN=https://myapp.com
// Before (Express + Webpack)
app.use(express.static("dist"));
app.get("/api/users", (req, res) => {
res.json(users);
});
// After (Bun fullstack)
serve({
routes: {
"/": homepage, // Replaces express.static
"/api/users": {
GET() {
return Response.json(users);
},
},
},
});
// Before (Next.js)
export default function handler(req, res) {
if (req.method === 'GET') {
res.json(users);
}
}
// After (Bun)
"/api/users": {
GET() { return Response.json(users); }
}
bun build CLI integration is not yet available for fullstack appsbun build CLIThis is a work in progress. Features and APIs may change as Bun continues to evolve.