---
title: Bun v0.2.0
description: Release notes for Bun v0.2.0
date: "2022-10-13T23:48:34Z"
author: jarred
thumbText: v0.2.0
bannerImage: "https://t4.ftcdn.net/jpg/04/91/94/47/360_F_491944758_CFmhrx1rcunEBlnn9Xc3q2keJ922fsff.jpg"
---

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 %}

## Introducing Bun v0.2.0

![https://user-images.githubusercontent.com/709451/195575815-96df744a-1073-4292-b24d-5ba76c20b942.png](https://user-images.githubusercontent.com/709451/195575815-96df744a-1073-4292-b24d-5ba76c20b942.png)

New:

- `bun --hot` brings hot reloading & zero-downtime restarts to Bun's JavaScript runtime
- `Bun.spawn` and `Bun.spawnSync` (process spawning API)
- `Request.body` - incoming HTTP request body streaming with `ReadableStream`
- _tons_ of bug fixes & reliability improvements to `Bun.serve` (HTTP server) and `fetch()` (HTTP client)
- Rewrote `setTimeout` and `setInterval` for better performance and reliability
- 2.7x+ lower memory usage for `Bun.serve` and anything using `Response` objects
- `"imports"` in package.json (`"#foo"` imports) works now https://github.com/oven-sh/bun/commit/21770eb0f31a43b3d6127ab957e271d029d6bc1b
- `"bun:test"` gets ~300x faster when using http server, websockets, etc https://github.com/oven-sh/bun/commit/524e48a81dfc6106ffcdd07b6fd035000b03146c
- Incrementally write files with `Bun.file(path).writer()`
- 30% faster Array.prototype.indexOf for strings (thanks @Constellation)
- 37% faster Array.prototype.map (thanks @Constellation)
- 1.4x - 4x faster String.prototype.substring (thanks @Constellation)
- 2.8x faster String.prototype.replace (thanks @Constellation)
- `new Blob(["hello world"])` is now [75x faster in Bun than Node](https://twitter.com/jarredsumner/status/1573204676782489600) - https://github.com/oven-sh/bun/commit/2c1926993bc4d94f9e7bc4d171217a707efd385c

Breaking:

- `bun run` and `bun` CLI arguments parsing has been changed so that anything after `bun run <file-or-script>` or `bun <file>` is passed through verbatim. This fixes a number of bugs with CLI argument parsing in both bun as a runtime and when used as a package.json `"scripts"` runner.

```bash
# before, server.js wouldn't see the --port argument
bun run server.js --port 3000
```

- `process.version` now reports a fake Node.js version instead of Bun's version. This is for compatibility with many npm packages that check for Node.js version to enable/disable features. To get Bun's version, use `Bun.version` or `process.versions.bun`.

- `Bun.serve().hostname` should return the hostname instead of the origin. This is a breaking change because it affects how URLs may be printed if you were using this getter before. https://github.com/oven-sh/bun/commit/e15fb6b9b220510df049e782d4f2f6eb3150d069

## `bun --hot`: hot reloads on the server

`bun --hot` lets you see code changes immediately, without restarting your server. Unlike popular file watchers like nodemon, `bun --hot` preserves some of the state of your app, meaning in-flight HTTP requests don't get interrupted.

{% image  alt="refresh speed comparison" src="https://user-images.githubusercontent.com/709451/195477632-5fd8a73e-014d-4589-9ba2-e075ad9eb040.gif" caption="Bun on the left, Nodemon on the right" /%}

To use it with Bun's HTTP server (automatic):

```ts
// The global object is preserved across code reloads
// You can use it to store state, for now until Bun implements import.meta.hot.
const reloadCount = globalThis.reloadCount || 0;
globalThis.reloadCount = reloadCount + 1;

export default {
  fetch(req: Request) {
    return new Response(`Code reloaded ${reloadCount} times`, {
      headers: { "content-type": "text/plain" },
    });
  },
};
```

Then, run:

```bash
bun --hot server.ts
```

You can also use `bun run`:

```bash
bun run --hot server.ts
```

For more information, see `bun --hot` section in Bun's readme.

## `Bun.spawn` spawn processes in Bun

`Bun.spawn` efficiently spawns a new process in Bun.

```ts
import { spawn } from "bun";

const { stdout } = await spawn(["echo", "hello world"]);
console.log(
  await new Response(
    // stdout is a ReadableStream
    stdout,
  ).text(),
); // "hello world"
```

`Bun.spawn` is flexible. `stdin` can be a `Response`, `Blob`, `Request`, `ArrayBuffer`, `ArrayBufferView`, `Bun.file`, `"pipe"` or `number`.

```ts
import { spawn } from "bun";

const { stdout } = spawn({
  cmd: ["esbuild"],
  // using fetch()
  stdin: await fetch(
    "https://raw.githubusercontent.com/oven-sh/bun/main/examples/hashing.js",
  ),
});

const text = await new Response(
  // stdout is a ReadableStream here
  stdout,
).text();
console.log(text.slice(0, 128), "..."); // const input = "hel...
```

`stdout` and `stderr` return `ReadableStream`s when `"pipe"` is used.

## Request.body & Response.body return a `ReadableStream`

This fixes https://github.com/oven-sh/bun/issues/530

You can read `Request` & `Response` objects bodies as a ReadableStream now

## `ReadableStream` now supports async iterators

This works now:

```ts
const body = new Response(["hello"]).body;
const chunks = [];
for await (const chunk of body) {
  chunks.push(chunk);
}
```

Previously, you had to call `getReader()` like this:

```ts
const reader = body.getReader();
const chunks = [];
while (true) {
  const { done, value } = await reader.read();
  if (done) {
    break;
  }
  chunks.push(value);
}
```

## HTTP request body streaming

`Bun.serve` now supports streaming request bodies. This is useful for large file uploads.

```ts
import { serve } from "bun";

serve({
  async fetch(req) {
    // body is a ReadableStream
    const body: ReadableStream = req.body;

    const id = `upload.${Date.now()}.txt`;
    const writer = Bun.file(id).writer();
    for await (const chunk of body) {
      writer.write(chunk);
    }
    const wrote = await writer.close();

    return Response.json({ wrote, id, type: req.headers.get("Content-Type") });
  },
});
```

## `"imports"` support in `package.json`

This release adds support for the [`imports` field in package.json](https://nodejs.org/api/packages.html#imports)

![image](https://user-images.githubusercontent.com/709451/195571807-b2991da1-1b4c-406f-be79-8c2a9a3b076c.png)

## Reduced memory usage for `Bun.serve()`

Bun wasn't correctly reporting memory usage for `Request`, `Response`, and `Blob` objects to JavaScriptCore, causing the garbage collector to be unaware of how much memory was really in use for http responses/requests.

![image](https://user-images.githubusercontent.com/709451/195571295-2a784d30-05b7-4fd2-bcb3-c82b6c70b37c.png)

## `bun:test` performance improvements

An event loop bug in `bun:test` caused the process the idle for awhile. Now Bun's own http server tests run > 10x faster.

![image](https://user-images.githubusercontent.com/709451/195572258-52e8e00a-420e-4616-a3c1-c47c4f68c69c.png)

### Bug fixes:

- Fix how console.log handle circular by [@zhiyuang](https://github.com/zhiyuang) in https://github.com/oven-sh/bun/pull/1293
- Fix nested modules bin executable issue by [@zhiyuang](https://github.com/zhiyuang) in https://github.com/oven-sh/bun/pull/1299
- Fix install error when node_modules already in npm package by [@zhiyuang](https://github.com/zhiyuang) in https://github.com/oven-sh/bun/pull/1301
- Fix fetch response redirected by [@zhiyuang](https://github.com/zhiyuang) in https://github.com/oven-sh/bun/pull/1303
- Fix occasional crash with .json() https://github.com/oven-sh/bun/commit/dfefb05b10e57e01faab0d633fc9538a571a566f
- Fix incorrect hostname logic in Bun.serve() https://github.com/oven-sh/bun/commit/167948f5c3afc0a4dc482222e42bd255951084ff
- Allow .env files to define the same key multiple times https://github.com/oven-sh/bun/commit/e94e6d8d95061c8bdb07ce96bc836689f49aafdd
- Fix crash when creating an empty array https://github.com/oven-sh/bun/commit/16b1e84138056774684b5e769a20dabd787d069c
- Fix console.log not printing an empty line https://github.com/oven-sh/bun/commit/b733125085a5746af121ce6d7b67eb45fb8e85e3
- Fix potential crash when TS code has an unexpected ")" https://github.com/oven-sh/bun/commit/a8ab18bd50b3a98c65c6ce96bd75d87d7893df12
- Support all ArrayBufferView in all hashing functions and node fs functions https://github.com/oven-sh/bun/commit/9d7bcac680c5f32d3fa89d9e47972957279a1a05
- Fix DotEnv Loader ignoring error log level - https://github.com/oven-sh/bun/commit/906e97223a3dd95801bc0d12f62314719c554fd6
- Fix missing path/posix and path/win32 https://github.com/oven-sh/bun/commit/dbccfc2b26371c921f3b3a55b03e8bb4a103444f
- Fix cancel not working in some cases in `ReadableStream`
- Fix crash in TextEncoder with rope strings that happens sometimes https://github.com/oven-sh/bun/commit/6b7a0c1d3fde32b6e3ded85456d0721c34aa9219
- `bun:sqlite` Fix crash in Database.deserialize
  https://github.com/oven-sh/bun/commit/9fd00727406b0170fa2d3bb43973ff8d78e7bb76
- Bun segfalts when tsconfig specifies a jsxFactory #1269
- unable to use EventEmitter with "require", empty object instead of a class #1284
- segmentation fault on "napi_wrap" when trying to call a loaded .node extension #1286
- "assert is not a function" error when calling the assert module as a function #941

More changes:

- `Bun.which(bin)`: find the path to a command
- `process` now extends `EventEmitter`
- Minor tweaks to `bun:test` output. now it includes "expect calls"

  {% image  width="279" alt="image" src="https://user-images.githubusercontent.com/709451/195565842-833615b9-b176-4363-ab48-c226c1bd722d.png" /%}

- `bun:test` print test failures at the bottom - https://github.com/oven-sh/bun/commit/c57b32fa0cdeaf7f1490bd6af9c5248a92c71ea0
- `navigator.userAgent` and `navigator.hardwareConcurrency` are now globals
- `require("tty").isatty` works now
- `require("fs").rm` works now
- Implement `console.count` and `console.countReset` - https://github.com/oven-sh/bun/commit/4060afb7c70dd3ba037bd23c813c22032e2dabe5
  ![image](https://user-images.githubusercontent.com/709451/195572709-67b8e7c7-1f5b-4ec8-922d-d4d249b5c379.png)
- Internal data structures for `fetch()` use 82% less memory (9.8 KB -> 1.8 KB)
- `Bun.version` reports Bun's version number
- `Bun.revision` reports the git commit SHA used at the time Bun was compiled

## All the PRs

- fix: add destination to ADD command in Dockerfile by [@DarthBenro008](https://github.com/DarthBenro008) in https://github.com/oven-sh/bun/pull/1268
- test: Promisify basic tests by [@albertpurnama](https://github.com/albertpurnama) in https://github.com/oven-sh/bun/pull/1018
- Add `body` to `Response` and `Request` by [@Jarred-Sumner](https://github.com/Jarred-Sumner) in https://github.com/oven-sh/bun/pull/1255
- Fix how console.log handle circular by [@zhiyuang](https://github.com/zhiyuang) in https://github.com/oven-sh/bun/pull/1293
- docs(thread_pool): comment readability improvements by [@ryanrussell](https://github.com/ryanrussell) in https://github.com/oven-sh/bun/pull/1241
- Fix nested modules bin executable issue by [@zhiyuang](https://github.com/zhiyuang) in https://github.com/oven-sh/bun/pull/1299
- Fix install error when node_modules already in npm package by [@zhiyuang](https://github.com/zhiyuang) in https://github.com/oven-sh/bun/pull/1301
- Fix fetch response redirected by [@zhiyuang](https://github.com/zhiyuang) in https://github.com/oven-sh/bun/pull/1303

## New Contributors

- @DarthBenro008 made their first contribution in https://github.com/oven-sh/bun/pull/1268
- @albertpurnama made their first contribution in https://github.com/oven-sh/bun/pull/1018
- @zhiyuang made their first contribution in https://github.com/oven-sh/bun/pull/1293

[**Full Changelog**](https://github.com/oven-sh/bun/compare/bun-v0.1.13...bun-v0.2.0)