To upgrade:

bun upgrade

What's new

• Type definitions for better editor integration and TypeScript LSP! There are types for the runtime APIs now in the bun-types npm package. A PR for @types/bun is waiting review (feel free to nudge them).
• Bun.serve() is a fast HTTP & HTTPS server that supports the Request and Response Web APIs. The server is a fork of uWebSockets
• Bun.write() – one API for writing files, pipes, and copying files leveraging the fastest system calls available for the input & platform. It uses the Blob Web API.
• Bun.mmap(path) lets you read files as a live-updating Uint8Array via the mmap(2) syscall. Thank you @evanwashere!!
• Bun.hash(bufferOrString) exposes fast non-cryptographic hashing functions. Useful for things like ETag, not for passwords.
• Bun.allocUnsafe(length) creates a new Uint8Array ~3.5x faster than new Uint8Array, but it is not zero-initialized. This is similar to Node's Buffer.allocUnsafe, though without the memory pool currently
• Several web APIs have been added, including URL
• A few more examples have been added to the examples folder
• Bug fixes to fs.read() and fs.write() and some more tests for fs
• Response.redirect(), Response.json(), and Response.error() have been added
• import.meta.url is now a file:// url string
• Bun.resolve and Bun.resolveSync let you resolve the same as import does. It throws a ResolveError on failure (same as import)
• Bun.stderr and Bun.stdout now return a Blob
• SharedArrayBuffer is now enabled (thanks @evanwashere!)
• Updated Next.js version

New Web APIs in bun.js

Going forward, Bun will first try to rely on WebKit/Safari's implementations of Web APIs rather than writing new ones. This will improve Web API compatibility while reducing bun's scope, without compromising performance

These Web APIs are now available in bun.js and powered by Safari's implementation:

• URL
• URLSearchParams
• ErrorEvent
• Event
• EventTarget
• DOMException
• Headers uses WebKit's implementation now instead of a custom one
• AbortSignal (not wired up to fetch or fs yet, it exists but not very useful)
• AbortController

Also added:

• reportError (does not dispatch an "error" event yet)

Additionally, all the builtin constructors in bun now have a .prototype property (this was missing before)

Bun.serve - fast HTTP server

For a hello world HTTP server that writes "bun!", Bun.serve serves about 2.5x more requests per second than node.js on Linux:

^{Bigger is better}

Code

Bun:

Bun.serve({
  fetch(req: Request) {
    return new Response(`bun!`);
  },
  port: 3000,
});

Node:

require("http")
  .createServer((req, res) => res.end("bun!"))
  .listen(8080);

Usage

Two ways to start an HTTP server with bun.js:

1. export default an object with a fetch function

If the file used to start bun has a default export with a fetch function, it will start the http server.

// hi.js
export default {
  fetch(req) {
    return new Response("HI!");
  },
};

// bun ./hi.js

fetch receives a Request object and must return either a Response or a Promise<Response>. In a future version, it might have an additional arguments for things like cookies.

2. Bun.serve starts the http server explicitly

Bun.serve({
  fetch(req) {
    return new Response("HI!");
  },
});

Error handling

For error handling, you get an error function.

If development: true and error is not defined or doesn't return a Response, you will get an exception page with a stack trace:

It will hopefully make it easier to debug issues with bun until bun gets debugger support. This error page is based on what bun dev does.

If the error function returns a Response, it will be served instead

Bun.serve({
  fetch(req) {
    throw new Error("woops!");
  },
  error(error: Error) {
    return new Response("Uh oh!!\n" + error.toString(), { status: 500 });
  },
});

If the error function itself throws and development is false, a generic 500 page will be shown

Currently, there is no way to stop the HTTP server once started 😅, but that will be added in a future version.

The interface for Bun.serve is based on what Cloudflare Workers does.

Bun.write() – optimizing I/O

Bun.write lets you write, copy or pipe files automatically using the fastest system calls compatible with the input and platform.

interface Bun {
  write(
    destination: string | number | FileBlob,
    input: string | FileBlob | Blob | ArrayBufferView
  ): Promise<number>;
}

All this complexity is handled by a single function.

// Write "Hello World" to output.txt
await Bun.write("output.txt", "Hello World");

// log a file to stdout
await Bun.write(Bun.stdout, Bun.file("input.txt"));

// write the HTTP response body to disk
await Bun.write("index.html", await fetch("http://example.com"));
// this does the same thing
await Bun.write(Bun.file("index.html"), await fetch("http://example.com"));

// copy input.txt to output.txt
await Bun.write("output.txt", Bun.file("input.txt"));

Bug fixes

• Fixed a bug on Linux where sometimes the HTTP thread would incorrectly go to sleep, causing requests to hang forever 😢 . Previously, it relied on data in the queues to determine whether it should idle and now it increments a counter.
• Fixed a bug that sometimes caused require to produce incorrect output depending on how the module was used
• Fixed a number of crashes in bun dev related to HMR & websockets - https://github.com/Jarred-Sumner/bun/commit/daeede28dbb3c6b5bb43250ca4f3524cd728ca4c
• fs.openSync now supports mode and flags - https://github.com/Jarred-Sumner/bun/commit/c73fcb073109405e1ccc30299bd9f8bef2791435
• fs.read and fs.write were incorrectly returning the output of fs/promises versions, this is fixed
• Fixed a crash that could occur during garbage collection when an fs function received a TypedArray as input. - https://github.com/Jarred-Sumner/bun/commit/614f64ba82947f7c2d3bf2dcc4e4993f6446e9b9. This also improves performance of sending array buffers to native a little
• Response's constructor previously read statusCode instead of status. This was incorrect and has been fixed.
• Fixed a bug where fs.stat reported incorrect information on macOS x64
• Slight improvement to HMR reliability if reading large files or slow filesystems over websockets - 89cd35f07fdb2e965e3518f3417e4c39f0163522
• Fixed a potential infinite loop when generating a sourcemap - fe973a5ab0d112ea6d80c8bcf7f693da879bb90d improve performance of accessing Bun.Transpiler and Bun.unsafe 29a759a65512278f1c20d1089ba05dbae268ef24