---
title: Bun v0.5.8
description: Introducing `expect()` snapshots in `bun test`, preloading modules using `bun --preload`, basic glob star support in bun install, improvements to Web & Node.js compatibility, lots of bug fixes, and a teaser of what's next.
date: "2023-03-18T00:00:00+00:00"
author: ashcon
thumbText: v0.5.8
---
Bun v0.5.8 introduces `expect()` snapshots in `bun test`, preloading modules using `bun --preload`, improvements to Web API & Node.js compatibility, lots of bug fixes, and a teaser of what's next.
{% codetabs %}
```sh#curl
$ curl -fsSL https://bun.sh/install | bash
```
```sh#npm
$ npm install -g bun
```
```sh#brew
$ brew tap oven-sh/bun
$ brew install bun
```
```sh#docker
$ docker pull oven/bun
$ docker run --rm --init --ulimit memlock=-1:-1 oven/bun
```
{% /codetabs %}
{% raw %}
{% /raw %}
To upgrade Bun:
```sh
$ bun upgrade
```
{% callout %}
We're hiring [C/C++ and Zig engineers](/careers) to build the future of JavaScript!
{% /callout %}
## Snapshot testing with `bun test`
[`bun test`](/docs/cli/test) aims to be a high-performance, drop-in replacement for Jest. Now it has support for snapshot testing, using [`expect(value).toMatchSnapshot()`](https://jestjs.io/docs/snapshot-testing#snapshot-testing-with-jest), which supports the same snapshot format as Jest. Here's how it works:
First, create a test.
```ts#snapshot.test.ts
import { test, expect } from "bun:test"; // "bun:test" imports are optional
test("can test a snapshot", async () => {
const response = await fetch("https://example.com/");
const body = await response.text();
expect(body).toMatchSnapshot();
});
```
Then, run the test file using `bun test`.
```sh
$ bun test snapshot.test.ts
```
Next, you'll see the following output in your terminal.
{% raw %}
snapshot.test.ts:
✓ can test a snapshot
1 pass
0 fail
snapshots: +1 added
1 expect() calls
Ran 1 tests across 1 files [48.00ms]
{% /raw %}
Finally, you'll see there is a newly-generated snapshot file. Bun uses the same snapshot format as Jest, which means **you don't need to re-generate your snapshots when migrating from Jest to [`bun test`](/docs/cli/test).**
```ts#__snapshots__/snapshot.test.ts.snap
exports[`can test a snapshot 1`] = `
"
Example Domain
"
`;
```
If you need to update your snapshots, you can pass the `--update-snapshots` flag, which will update snaphots for every test file that is run.
```sh
$ bun test --update-snapshots
```
In addition to `toMatchSnapshot()`, Bun now supports these new matchers:
- [`toThrow(RegExp)`](https://jestjs.io/docs/expect#tothrowerror) (in addition to `toThrow(string|Error)`)
- [`toBeInstanceOf()`](https://jestjs.io/docs/expect#tobeinstanceofclass) (thanks to [@zhiyuang](https://github.com/zhiyuang))
- [`toMatch()`](https://jestjs.io/docs/expect#tomatchregexp--string) (thanks to [@zhiyuang](https://github.com/zhiyuang))
We also added a flag to re-run a test file multiple times, to help with reproducing errors in flaky tests.
```sh
bun test --rerun-each=5
```
This reruns each test file 5 times.
## `bun --preload [command]`
Bun can now preload files before running a file or a test suite. This behavior is analogous to [`node --require`](https://nodejs.org/api/cli.html#-r---require-module).
To preload a file via the `--preload` flag:
```bash
$ bun --preload ./preload.ts run ./index.ts
```
To configure a list of files to `preload` in `bunfig.toml`:
```toml#bunfig.toml
preload = ["./preload.ts"]
```
This is useful for registering [`plugins`](https://bun.sh/docs/runtime/plugins#usage), injecting globals, or performing setup tasks without cluttering your scripts or entrypoints with extra `import()` or `require()` statements.
Here's an example of how to preload a `Bun.plugin()` to load `.yml` files.
{% codetabs %}
```ts#index.ts
import config from "./config.yml";
console.log(config);
```
```yaml#config.yml
enabled: true
```
```ts#yaml.plugin.ts
import { plugin } from "bun";
plugin({
name: "YAML",
async setup(build) {
const { load } = await import("js-yaml");
const { readFileSync } = await import("fs");
// when a .yaml file is imported...
build.onLoad({ filter: /\.(yaml|yml)$/ }, (args) => {
// read and parse the file
const text = readFileSync(args.path, "utf8");
const exports = load(text) as Record;
// and returns it as a module
return {
exports: {default: exports, ...exports},
loader: "object", // special loader for JS objects
};
});
},
});
```
{% /codetabs %}
You can now import `.yml` files from your entrypoint:
```sh
$ bun --preload ./yaml.plugin.ts index.ts
{
enabled: true
}
```
To avoid the `--preload` flag, configure `bunfig.toml`:
```toml#bunfig.toml
preload = ["./yaml.plugin.ts"]
```
Running `bun test` or `bun run` will now preload the plugin automatically.
```sh
$ bun run index.ts
{
enabled: true
}
```
{% /codetabs %}
## Partial glob support in `bun install` `workspaces`
The following pattern is now supported in `"workspaces"` with bun install:
```jsonc
{
"name": "myWorkspace",
"workspaces": [
// Make all folders with a package.json and a name in packages/ part of the workspace
"packages/*"
]
}
```
You can use a `/*` to add all folders matching the prefix into your workspace. This is useful for monorepos that have many packages.
> For now, only a single glob pattern at the very end (`foo/*`) is supported. We plan to improve our glob support in the future. In the meantime, we also added better error messages when a glob pattern isn't implemented yet.
## Web Compatibility
Thanks to improvements to Bun's test coverage, we've fixed a number of bugs in Bun's Web API compatibility.
### `request.bodyUsed` & `response.bodyUsed`
[`request.bodyUsed`](https://developer.mozilla.org/en-US/docs/Web/API/Request/bodyUsed) and [`response.bodyUsed`](https://developer.mozilla.org/en-US/docs/Web/API/Response/bodyUsed) were inconsistent with the spec when using `null` or `undefined` bodies.
```js
const response = new Response(null);
await response.arrayBuffer();
console.log(response.bodyUsed);
/*
Incorrect:
Bun v0.5.7: true
Correct:
Bun v0.5.8: false
Chrome: false
Safari: false
*/
```
### Consuming `Request` & `Response` bodies
`null` or `undefined` [`Request`](https://developer.mozilla.org/en-US/docs/Web/API/Request) & [`Response`](https://developer.mozilla.org/en-US/docs/Web/API/Response) bodies can now be consumed multiple times, which aligns the behavior with Chrome & Safari.
Previously, Bun would throw an error when trying to consume a `null` or `undefined` body twice:
```bash
$ bun-0.5.7 response.js
1 | const response = new Response(null);
2 | await response.arrayBuffer();
3 | console.log(await response.arrayBuffer());
^
error: Body already used
```
Now `.arrayBuffer()` on `null` or `undefined` body returns an empty [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) instead:
```bash
$ bun response.js
ArrayBuffer(0) [ ]
/*
Incorrect:
Bun v0.5.7: "Body already used"
Correct:
Bun v0.5.8: ArrayBuffer(0) [ ]
Chrome: ArrayBuffer(0) [ ]
Safari: ArrayBuffer(0) [ ]
*/
```
Similarly, [`Response.prototype.body`](https://developer.mozilla.org/en-US/docs/Web/API/Response/body) is supposed to return `null` when there is no body, but Bun was returning an empty [`ReadableStream`](https://developer.mozilla.org/en-US/docs/Web/API/ReadableStream) instead.
```js
const response = new Response(null);
console.log(response.body);
/*
Incorrect:
Bun v0.5.7: ReadableStream { ... }
Correct:
Bun v0.5.8: null
Chrome: null
Safari: null
*/
```
### `blob.slice()` `contentType` argument
[`blob.slice`](https://developer.mozilla.org/en-US/docs/Web/API/Blob/slice) accepts an optional third argument for the `type` of the new [`Blob`](https://developer.mozilla.org/en-US/docs/Web/API/Blob). Previously, Bun didn't support this argument.
```ts
const blob = new Blob(["Hello, world!"], { type: "text/plain" });
const slice = blob.slice(0, 5, "text/html; charset=utf-8");
console.log(slice.type); // "text/html; charset=utf-8"
/*
Incorrect:
Bun v0.5.7: ""
Correct:
Bun v0.5.8: "text/html; charset=utf-8"
Chrome: "text/html; charset=utf-8"
Safari: "text/html; charset=utf-8"
*/
```
### `Request` constructor
The [`Request`](https://developer.mozilla.org/en-US/docs/Web/API/Request) constructor in Bun had a couple bugs.
When given two arguments, it always expected the first argument to be a string, which is incorrect.
```js
// This didn't work: (inconsistent with the spec)
new Request(new Request("https://example.com"), {});
// But any of these did:
new Request(new Request("https://example.com"));
new Request("https://example.com", { method: "POST" });
new Request("https://example.com", {});
```
That has been fixed, and now the first argument can be a string or a [`Request`](https://developer.mozilla.org/en-US/docs/Web/API/Request) object.
```js
// This works now:
console.log(new Request(new Request("https://example.com"), {}).url);
// "https://example.com"
```
Another bug: the `url` argument was not being validated correctly (validated in `fetch()` but not in `new Request()`)
```ts
// this is supposed to throw:
const request = new Request("", { method: "POST" });
```
Now it (correctly) throws an error:
```bash
$ bun /tmp/app.js
1 | const request = new Request("", { method: "POST" });
^
error: Failed to construct 'Request': url is required.
```
Bun's test coverage for the `Request` constructor was lacking and Bun's implementation of `fetch` (which does validate) doesn't use the same code path as the `Request` constructor.
## Node.js compatibility
Bun continues to make improvements to Node.js compatibility. Here's what has changed since the last release.
- [Dramatically](https://github.com/oven-sh/bun/pull/2341) improved [`Buffer`](https://nodejs.org/api/buffer.html#buffer) implementation and is now passing many more Node.js tests
- Implemented [`os.cpus()`](https://nodejs.org/api/os.html#oscpus) for macOS (previously, was only supported on Linux)
- Implemented [`os.networkInterfaces()`](https://nodejs.org/api/os.html#osnetworkinterfaces)
- Added [`AbortSignal`](https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal) support to [`http.Server`](https://nodejs.org/api/http.html#class-httpserver) and [`http.ClientRequest`](https://nodejs.org/api/http.html#class-httpclientrequest)
- `node:net`'s server function `listen` callback now fires after the server is listening, instead of sometimes firing before the server is listening
- `node:zlib` was missing the export for `constants`
## `Bun.sleepSync()`
To fix an inconsistency issue between [`Bun.sleep()`](/docs/api/utils#bun-sleep) and `Bun.sleepSync()`, there is a **breaking change** where `Bun.sleepSync()` now accepts milliseconds, instead of seconds. Using code search on GitHub, we found that most usages were already assuming the units were milliseconds.
```ts
Bun.sleepSync(1); // sleep for 1 ms (not recommended)
await Bun.sleep(1); // sleep for 1 ms (recommended)
```
## What's next?
For Bun v0.6, you can expect big changes, including a brand new bundler!
{% raw %}
{% /raw %}
Bun's upcoming bundler intends to make building modern, full-stack JavaScript and TypeScript apps a lot simpler (and faster).
Of course, we continue to make progress towards our priorities of Node.js compatibility, overall stability, and performance as Bun inches closer to a 1.0 release. To measure progress towards these goals we've dramatically increased our test coverage of Bun, Node.js, and standard-Web APIs. Stay tunned.
## Changelog
{% table %}
---
- [`#2156`](https://github.com/oven-sh/bun/pull/2156)
- Fixed `{Request,Response}.body` not being null by [@cirospaciari](https://github.com/cirospaciari)
---
- [`#2115`](https://github.com/oven-sh/bun/pull/2115)
- Implemented `os.cpus()` for macOS by [@jwhear](https://github.com/jwhear)
---
- [`#2161`](https://github.com/oven-sh/bun/pull/2161)
- Fixed `HTMLRewriter.onDocument()` not being run by [@jwhear](https://github.com/jwhear)
---
- [`#2144`](https://github.com/oven-sh/bun/pull/2144)
- Fixed incorrect return value for `dns.{resolve4,resolve6}()` by [@cirospaciari](https://github.com/cirospaciari)
---
- [`599f63c`](https://github.com/oven-sh/bun/commit/599f63c2047b5adcc3cd774a8ad89a52150d24b2)
- Supported older releases of macOS, including 10.15 by [@Jarred-Sumner](https://github.com/Jarred-Sumner)
---
- [`0a7309c`](https://github.com/oven-sh/bun/commit/0a7309c8f27e5e3344b3b121559168b98dd33fee)
- Improved performance of `EventEmitter` by [@Jarred-Sumner](https://github.com/Jarred-Sumner)
---
- [`eb94e5b`](https://github.com/oven-sh/bun/commit/eb94e5b990577e752f6f07aa7014f985c9dcce91)
- Changed BoringSSL to use heap from mimalloc by [@Jarred-Sumner](https://github.com/Jarred-Sumner)
---
- [`#2192`](https://github.com/oven-sh/bun/pull/2192)
- Improved stability of `bun pm ls` by [@alexlamsl](https://github.com/alexlamsl)
---
- [`693be3d`](https://github.com/oven-sh/bun/commit/693be3d1c2fe63cb5961a0023ad4c301209495bc)
- Improved performance of ASCII case-insensitive comparisons by [@Jarred-Sumner](https://github.com/Jarred-Sumner)
---
- [`#2202`](https://github.com/oven-sh/bun/pull/2202)
- Fixed ANSI escape codes not being piped from stdout to a file by [@alexlamsl](https://github.com/alexlamsl)
---
- [`5d296f6`](https://github.com/oven-sh/bun/commit/5d296f6228175097e59848416b1a3844bde940b1)
- Fixed an issue where shasum was being parsed twice by [@Jarred-Sumner](https://github.com/Jarred-Sumner)
---
- [`#2213`](https://github.com/oven-sh/bun/pull/2213)
- Fixed an issue with `bun install` and duplicate dependencies by [@alexlamsl](https://github.com/alexlamsl)
---
- [`#2142`](https://github.com/oven-sh/bun/pull/2142)
- Implemented `os.networkInterfaces()` by [@jwhear](https://github.com/jwhear)
---
- [`#2191`](https://github.com/oven-sh/bun/pull/2191)
- Fixed incorrect port for `bun dev` by [@xjmdoo](https://github.com/xjmdoo)
---
- [`#2143`](https://github.com/oven-sh/bun/pull/2143)
- Fixed issues with `fetch({ signal })` on shutdown by [@cirospaciari](https://github.com/cirospaciari)
---
- [`#2223`](https://github.com/oven-sh/bun/pull/2223)
- Implemented `http.listen({ signal })` by [@cirospaciari](https://github.com/cirospaciari)
---
- [`#2222`](https://github.com/oven-sh/bun/pull/2222)
- Implemented `http.get({ signal })` by [@cirospaciari](https://github.com/cirospaciari)
---
- [`#2226`](https://github.com/oven-sh/bun/pull/2226)
- Removed transient error when sqlite was given an empty statement by [@ThatOneBro](https://github.com/ThatOneBro)
---
- [`#2231`](https://github.com/oven-sh/bun/pull/2231)
- Implemented `bun --preload ` by [@Jarred-Sumner](https://github.com/Jarred-Sumner)
---
- [`#2249`](https://github.com/oven-sh/bun/pull/2249)
- Fixed issue with `Bun.file().arrayBuffer()` on an empty file by [@cirospaciari](https://github.com/cirospaciari)
---
- [`#2258`](https://github.com/oven-sh/bun/pull/2258)
- Fixed bug where `http.request()` did not accept `URL`s by [@ThatOneBro](https://github.com/ThatOneBro)
---
- [`#2262`](https://github.com/oven-sh/bun/pull/2262)
- Improved compatibility of `http.request()` when method is GET or HEAD and has a body by [@ThatOneBro](https://github.com/ThatOneBro)
---
- [`#2242`](https://github.com/oven-sh/bun/pull/2242)
- **[BREAKING]** `Bun.sleepSync()` now takes milliseconds, instead of seconds by [@jwhear](https://github.com/jwhear)
---
- [`#2276`](https://github.com/oven-sh/bun/pull/2276)
- Fixed `os.tmpdir()` from removing trailing slashing by [@cirospaciari](https://github.com/cirospaciari)
---
- [`#2285`](https://github.com/oven-sh/bun/pull/2285)
- Fixed `request.url` not including search params in `node:http` by [@zhiyuang](https://github.com/zhiyuang)
---
- [`#2295`](https://github.com/oven-sh/bun/pull/2295)
- Changed `bunx` without parameters to show a help page by [@Zeko369](https://github.com/Zeko369)
---
- [`#2288`](https://github.com/oven-sh/bun/pull/2288)
- Fixed headers not being lowercase in `node:http` by [@ThatOneBro](https://github.com/ThatOneBro)
---
- [`#2293`](https://github.com/oven-sh/bun/pull/2293)
- Fixed `bunx` from not being able to find scoped npm packages by [@Zeko369](https://github.com/Zeko369)
---
- [`#2302`](https://github.com/oven-sh/bun/pull/2302)
- Fixed an issue where "latest" would not be considered in semver range by [@alexlamsl](https://github.com/alexlamsl)
---
- [`#2307`](https://github.com/oven-sh/bun/pull/2307)
- Fixed `bun install` not reporting connection errors to the npm registry by [@alexlamsl](https://github.com/alexlamsl)
---
- [`#2314`](https://github.com/oven-sh/bun/pull/2314)
- Implemented `expect().toThrow(RegExp)` by [@alexlamsl](https://github.com/alexlamsl)
---
- [`#2315`](https://github.com/oven-sh/bun/pull/2315)
- Fixed error messages for `Blob` on Linux by [@alexlamsl](https://github.com/alexlamsl)
---
- [`#2320`](https://github.com/oven-sh/bun/pull/2320)
- Implemented some of `tty.WriteStream` for `process.{stdout,stderr}` by [@ThatOneBro](https://github.com/ThatOneBro)
---
- [`0a9cb0e`](https://github.com/oven-sh/bun/commit/0a9cb0e13aba18c51eebcd4e246ac2620fac2fbc)
- Fixed issues when `HTMLRewriter` would receive an empty string by [@Jarred-Sumner](https://github.com/Jarred-Sumner)
---
- [`#2331`](https://github.com/oven-sh/bun/pull/2331)
- Fixed parameter errors with `crypto.scryptSync()` by [@dylan-conway](https://github.com/dylan-conway)
---
- [`#2341`](https://github.com/oven-sh/bun/pull/2341)
- Improved `Buffer` compatibility with Node.js by [@alexlamsl](https://github.com/alexlamsl)
---
- [`e16053c`](https://github.com/oven-sh/bun/commit/e16053c39ed18fb7024159d7e8bc58e5120bbf34)
- Fixed an issue where `crypto.createHash().update("binary")` would not work by [@Jarred-Sumner](https://github.com/Jarred-Sumner)
---
- [`#2340`](https://github.com/oven-sh/bun/pull/2340)
- Improved spec-compliance of `Blob.type` by [@Jarred-Sumner](https://github.com/Jarred-Sumner)
---
- [`#2371`](https://github.com/oven-sh/bun/pull/2371)
- Fixed error when `require.resolve()` argument is empty by [@paperclover](https://github.com/paperclover)
---
- [`#2337`](https://github.com/oven-sh/bun/pull/2337)
- Implemented unix socket support in `net.Server` by [@cirospaciari](https://github.com/cirospaciari)
---
- [`4c38798`](https://github.com/oven-sh/bun/commit/4c3879814289f79d81aef30e55c4bad9145c2af8)
- Fixed incorrect encoding of `Socket.remoteAddress` by [@Jarred-Sumner](https://github.com/Jarred-Sumner)
---
- [`27f5012`](https://github.com/oven-sh/bun/commit/27f5012f50b998fec5b45531de2439a11a72eaa2)
- Fixed `node:https` from being readonly by [@Jarred-Sumner](https://github.com/Jarred-Sumner)
---
- [`#2389`](https://github.com/oven-sh/bun/pull/2389)
- Implemented `expect().toBeInstanceOf()` by [@zhiyuang](https://github.com/zhiyuang)
---
- [`e613b50`](https://github.com/oven-sh/bun/commit/e613b501e218737cd9fc7a957f3ab65aee58a156)
- Implemented missing `constants` in `node:zlib` by [@Jarred-Sumner](https://github.com/Jarred-Sumner)
---
- [`#2294`](https://github.com/oven-sh/bun/pull/2294)
- Implemented `expect().toMatchSnapshot()` by [@dylan-conway](https://github.com/dylan-conway)
---
- [`#2397`](https://github.com/oven-sh/bun/pull/2397)
- Fixed an issue where parsing a malformed `bun.lockb` by [@alexlamsl](https://github.com/alexlamsl)
---
- [`#2400`](https://github.com/oven-sh/bun/pull/2400)
- Fixed an issue where `Bun.serve()` could not listen on IPv6 by [@cirospaciari](https://github.com/cirospaciari)
---
- [`9a5f78f`](https://github.com/oven-sh/bun/commit/9a5f78fa3bdc7d841067332480a37b9faa7ff70e)
- Fixed `console.log()` not showing `[Getter]` values by [@Jarred-Sumner](https://github.com/Jarred-Sumner)
---
- [`#2404`](https://github.com/oven-sh/bun/pull/2404)
- Implemented `expect().toMatch(RegExp)` by [@zhiyuang](https://github.com/zhiyuang)
---
===================
{% /table %}
Also, if you haven't heard, [Bun has docs now!](/docs)
A huge thanks to [@colinhacks](https://github.com/colinhacks), as well as the many folks that have contributed since the last release: [@jakeboone02](https://github.com/jakeboone02), [@charliermarsh](https://github.com/charliermarsh), [@BrettBlox](https://github.com/BrettBlox), [@damianstasik](https://github.com/damianstasik), [@Sheraff](https://github.com/Sheraff), [@johnnyreilly](https://github.com/johnnyreilly), [@fdaciuk](https://github.com/fdaciuk), [@akash-joshi](https://github.com/akash-joshi), [@TommasoAmici](https://github.com/TommasoAmici), [@raxityo](https://github.com/raxityo), [@DreierF](https://github.com/DreierF), [@rmorey](https://github.com/rmorey), [@cunzaizhuyi](https://github.com/cunzaizhuyi), [@rodoabad](https://github.com/rodoabad), [@gaurishhs](https://github.com/gaurishhs), [@maor-benami](https://github.com/maor-benami), [@aabccd021](https://github.com/aabccd021), [@pfgithub](https://github.com/pfgithub), [@bushuai](https://github.com/bushuai), [@Zeko369](https://github.com/Zeko369), [@noahmarro](https://github.com/noahmarro), [@harisvsulaiman](https://github.com/harisvsulaiman), [@nskins](https://github.com/nskins), [@milesj](https://github.com/milesj), and [@jsoref](https://github.com/jsoref).