---
title: Bun v0.2.1
description: Release notes for Bun v0.2.1
date: "2022-10-19T06:10:52Z"
author: jarred
thumbText: v0.2.1
---

To upgrade:

```bash
bun upgrade
```

To install:

```bash
curl https://bun.sh/install | bash
```

{% details summary="If you have any problems upgrading" %}

Run the install script (you can run it multiple times):

```bash
curl https://bun.sh/install | bash
```

{% /details %}

## WebSocket server

`Bun.serve()` now has builtin support for websockets on the server

```ts
Bun.serve({
  websocket: {
    message(ws, message) {
      ws.send(message);
    },
  },

  fetch(req, server) {
    // Upgrade to a ServerWebSocket if we can
    // This automatically checks for the `Sec-WebSocket-Key` header
    // meaning you don't have to check headers, you can just call `upgrade()`
    if (server.upgrade(req))
      // When upgrading, we return undefined since we don't want to send a Response
      return;

    return new Response("Regular HTTP response");
  },
});
```

For more information about using websockets with `Bun.serve()`, [see the readme](https://github.com/oven-sh/bun#websockets-with-bunserve)

For a chat room on Linux:

{% image width="440" alt="chat room benchmark linux" src="https://user-images.githubusercontent.com/709451/196610254-5d49703a-ddc3-4010-82be-1e99d24d4123.png" /%}

To reproduce this benchmark on your own computer, [go here](https://github.com/oven-sh/bun/tree/main/bench/websocket-server)

Bun's server-side websockets are powered by [uWebSockets](https://github.com/uNetworking/uWebSockets).

## RegExp lookbehinds assertions fix

To address #314, Bun now includes a fallback RegExp implementation that uses the [Oniguruma](https://github.com/kkos/oniguruma) regex engine. Thanks to [@dylan-conway](https://github.com/dylan-conway)!

RegExp lookbehind assertions are used by popular npm packages like Discord.js

When a RegExp literal with a lookbehind is used inside Bun's runtime, Bun's transpiler now automatically replaces it with a `Bun.OnigurumaRegExp`. This API isn't intended to be used outside of the transpiler and will be removed once [JavaScriptCore lands native support](https://bugs.webkit.org/show_bug.cgi?id=174931).

When run inside Bun's JavaScript runtime, this input:

```js
export default /\d+(?=%)/;
```

Transpiles to:

```js
export default new globalThis.Bun.OnigurumaRegExp("\\d+(?=%)");
```

The RegExp polyfill is largely based on JavaScriptCore's own `JSC::RegExp` bindings.

## More stuff

- Send a `Date` header in HTTP responses
- [`performance.timeOrigin`]() has been implemented
- `process.argv` was returning an empty array when bun started without arguments other than the script, like `bun foo.js` (thanks to [@dylan-conway](https://github.com/dylan-conway) for the fix)
- [Fix a crash when BodyMixin functions throw](https://github.com/oven-sh/bun/commit/3482d761758368c74d4971f75606af5657aff53c)
- [Fix a memory leak in HTTP server related to promises](https://github.com/oven-sh/bun/commit/b1e97edc59628a1ae5ae02547947722ca96761c3)
- Fix a regression from v0.2.0 where small buffered (non-streaming) HTTP response bodies would sometimes include invalid data due to a memory aliasing bug
- Fix a bug where a pong control frame in Bun's `WebSocket` client would sometimes put the `WebSocket` in an error state https://github.com/oven-sh/bun/commit/c6fe82018aeda88a3337a5355313de7db68ef827
- Fix a bug where a `WebSocket` client would not keep the process open - #1335
- More test coverage for Bun's client-side `WebSocket` implementation due to adding server-side WebSockets
- Added DOMJIT function call support to Bun's JavaScriptCore bindings generator (used by the new `ServerWebSocket` object for `publishText`, `publishBinary`, `sendText` and `sendBinary` functions)

[**Full Changelog**](https://github.com/oven-sh/bun/compare/bun-v0.2.0...bun-v0.2.1)