Bun v0.7.3

Jarred Sumner · August 6, 2023

Bun v0.7.3 adds support for code coverage and filtering tests by RegExp pattern. Bugs have been fixed in async Node.js fs functions, bun:sqlite, Buffer.prototype.copy, and macros.

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Bun is an incredibly fast JavaScript runtime, bundler, transpiler, and package manager — all in one. Over the past couple months, we've been releasing a lot of changes to Bun recently, here's a recap in case you missed it:

  • v0.6.13 - Implemented mock Date, faster base64 encoding, and fixes for WebSocket and node:tls.
  • v0.6.14 - process.memoryUsage(), process.cpuUsage(), process.on('beforeExit', cb), process.on('exit', cb) and crash fixes
  • v0.7.0 - Web Workers, --smol, structuredClone(), WebSocket reliability improvements, node:tls fixes, and more.
  • v0.7.1 - ES Modules load 30% - 250% faster, fs.watch fixes, and lots of node:fs compatibility improvements.
  • v0.7.2 - node:worker_threads, node:diagnostics_channel, BroadcastChannel, Node.js compatibility improvements, fixes to a couple memory leaks

To install Bun:

curl -fsSL https://bun.sh/install | bash
npm install -g bun
brew tap oven-sh/bun
brew install bun
docker pull oven/bun
docker run --rm --init --ulimit memlock=-1:-1 oven/bun

To upgrade Bun:

bun upgrade

Code coverage reporting in bun test

bun test now has builtin suppport for code coverage reporting. To enable it, pass the --coverage flag:

bun test --coverage

This will generate a textual report in the terminal.

File         | % Funcs | % Lines | Uncovered Line #s
All files    |   38.89 |   42.11 |
 index-0.ts  |   33.33 |   36.84 | 10-15,19-24
 index-1.ts  |   33.33 |   36.84 | 10-15,19-24
 index-10.ts |   33.33 |   36.84 | 10-15,19-24
 index-2.ts  |   33.33 |   36.84 | 10-15,19-24
 index-3.ts  |   33.33 |   36.84 | 10-15,19-24
 index-4.ts  |   33.33 |   36.84 | 10-15,19-24
 index-5.ts  |   33.33 |   36.84 | 10-15,19-24
 index-6.ts  |   33.33 |   36.84 | 10-15,19-24
 index-7.ts  |   33.33 |   36.84 | 10-15,19-24
 index-8.ts  |   33.33 |   36.84 | 10-15,19-24
 index-9.ts  |   33.33 |   36.84 | 10-15,19-24
 index.ts    |  100.00 |  100.00 |

A more detailed serialized report is planned in a future release.

Filter tests by RegExp pattern

bun test now supports filtering tests by name with a RegExp pattern. To filter tests, pass the -t flag:

bun test -t /foo/

This will run all tests that match the /foo/ pattern.

bun --hot now clears the terminal on reload

Thanks to @simylein.

Bun.plugin no longer uses transpiler magic

The recommended way to use Bun.plugin is now with --preload, to ensure that the plugin is loaded before any other code.

// my markdown plugin
import { plugin, file } from "bun";

  name: "Markdown",
  async setup(builder) {
    builder.onLoad({ filter: /\.(md)$/ }, async ({ path }) => {
      console.log(`[markdown-loader] ${path}`);
      const contents = await file(path).text();
      const slug = path.split("/").slice(-1)[0].slice(0, -3);
      return {
        exports: {
        loader: "object",

Previously, Bun would inject the plugin ahead of time so that the plugin could potentially be used in the same file as the plugin was defined in. This caused... problems.

Now plugins have to be loaded with --preload or by configuring preload in bunfig.toml.

Node.js compatibilty improvements


The node:dns module now exports dns.getServers(), which returns an array of IP addresses as strings. Thanks to @Hanaasagi.

import dns from "node:dns";
import fs from "node:fs";
import os from "node:os";

test("dns.getServers", (done) => {
  function parseResolvConf() {
    let servers = [];
    try {
      const content = fs.readFileSync("/etc/resolv.conf", "utf-8");
      const lines = content.split(os.EOL);

      for (const line of lines) {
        const parts = line.trim().split(/\s+/);
        if (parts.length >= 2 && parts[0] === "nameserver") {
    } catch (err) {
    return servers;

  const expectServers = parseResolvConf();
  const actualServers = dns.getServers();
  try {
    for (const server of expectServers) {
  } catch (err) {
    return done(err);

Buffer.copy bugfix

Previously, the following test would fail in Bun but pass in Node.js:

it("should ignore sourceEnd if it's out of range", () => {
  const buf1 = Buffer.allocUnsafe(26);
  const buf2 = Buffer.allocUnsafe(10).fill("!");

  for (let i = 0; i < 26; i++) {
    // 97 is the decimal ASCII value for 'a'.
    buf1[i] = i + 97;

  // Copy `buf1` bytes "xyz" into `buf2` starting at byte 1 of `buf2`.
  expect(buf1.copy(buf2, 1, 23, 100)).toBe(3);

This has been fixed, thanks to @buffaybu.


The node:module module now exports Module.wrap(code), which is an undocumented function used by Webpack.

Bug fixes

We've also fixed a number of bugs.

Crash in bun:sqlite

A crash in bun:sqlite was introduced after upgrading JavaScriptCore in Bun v0.7.2 (not JavaScriptCore's fault, our fault). This has been fixed.

This crash happened when columns returned strings greater than 64 characters.

Crash in async Node.js fs functions

A thread-safety issue in the async version of Node.js fs functions was fixed in this release. Sometimes strings are threadlocal (such as when they come from property names) and passing them to another thread causes unexpected behavior. Bun's fs functions now clones threadlocal strings before they are passed to another thread. This addresses the bug without introducing a performance regression.

bun init now accepts a nested directory path

Thanks to @Hanaasagi, bun init now accepts a directory path. This allows you to initialize a Bun project in a directory other than the current working directory.

bun init ./foo/my-project

workspace:* dependencies bug fix

A bug caused workspace:* dependencies to be incorrectly not found in certain cases. This has been fixed thanks to @alexlamsl.

Event, DOMException, ErrorEvent, etc are writable

The following Web API globals are now writable:

This fixes a bug impacting Angular server-side rendering support.

Thanks to @arturovt for fixing this.


View the complete changelog