Bun v1.3.11 | Bun Blog

curl -fsSL https://bun.sh/install | bash

npm install -g bun

powershell -c "irm bun.sh/install.ps1|iex"

scoop install bun

brew tap oven-sh/bun

brew install bun

docker pull oven/bun

docker run --rm --init --ulimit memlock=-1:-1 oven/bun

bun upgrade

In the next version of Bun

Bun gets 4 MB smaller on Linux x64 because we deleted CMake pic.twitter.com/HQPacwNO3O

Bun now includes a built-in Bun.cron API for registering OS-level cron jobs, parsing cron expressions, and removing scheduled jobs — all cross-platform.

// Register a cron job (crontab on Linux, launchd on macOS, Task Scheduler on Windows)
await Bun.cron("./worker.ts", "30 2 * * MON", "weekly-report");

When the OS scheduler fires, Bun imports the script and calls default.scheduled(), following the Cloudflare Workers Cron Triggers API:

// worker.ts
export default {
async scheduled(controller) {
// controller.cron === "30 2 * * 1"
// controller.scheduledTime === 1737340200000
await doWork();
},
};

const next = Bun.cron.parse("*/15 * * * *"); // next quarter-hour
const weekday = Bun.cron.parse("0 9 * * MON-FRI"); // next weekday at 9 AM UTC
const yearly = Bun.cron.parse("@yearly"); // next January 1st

// Chain calls to get a sequence
const first = Bun.cron.parse("0 * * * *", from);
const second = Bun.cron.parse("0 * * * *", first);

Returns a Date or null if no match exists within ~4 years (e.g. February 30th).

await Bun.cron.remove("weekly-report");

Re-registering with the same title overwrites the existing job in-place.

A new built-in that replaces both the slice-ansi and cli-truncate npm packages. Bun.sliceAnsi slices strings by terminal column width while preserving ANSI escape codes (SGR colors, OSC 8 hyperlinks) and respecting grapheme cluster boundaries (emoji, combining marks, flags).

// Plain slice (replaces slice-ansi)
Bun.sliceAnsi("\x1b[31mhello\x1b[39m", 1, 4); // "\x1b[31mell\x1b[39m"

// Truncation with ellipsis (replaces cli-truncate)
Bun.sliceAnsi("unicorn", 0, 4, "…"); // "uni…"
Bun.sliceAnsi("unicorn", -4, undefined, "…"); // "…orn"

The ellipsis is emitted inside active SGR styles (inherits color/bold) so truncated text stays visually consistent, but outside hyperlinks to avoid broken links. Negative indices are supported for slicing from the end.

An optional { ambiguousIsNarrow } option is available for controlling East Asian ambiguous width behavior, matching Bun.stringWidth and Bun.wrapAnsi.

Uses a three-tier dispatch strategy:

The listItem callback in Bun.markdown.render() now receives index, depth, ordered, and start in its metadata object, and the list callback now includes depth. Previously, listItem only received checked (and only for task list items), making it impossible to know an item's position, nesting level, or parent list type without workarounds.

This makes it straightforward to implement custom list markers like nested numbering schemes (1. / a. / i.) without regex post-processing:

const result = Bun.markdown.render(
"1. first\n 1. sub-a\n 2. sub-b\n2. second",
{
listItem: (children, { index, depth, ordered, start }) => {
const n = (start ?? 1) + index;
const marker = !ordered
? "-"
: depth === 0
? `${n}.`
: `${String.fromCharCode(96 + n)}.`;
return " ".repeat(depth) + marker + " " + children.trimEnd() + "\n";
},
list: (children) => "\n" + children,
},
);
// 1. first
// a. sub-a
// b. sub-b
// 2. second

The full listItem meta shape is now:

Breaking change: The listItem callback now always receives the meta object (previously it was only passed for task list items). start and checked are undefined when not applicable, keeping the object shape fixed for monomorphic inline caches.

Meta objects use cached JSC structures internally, adding ~0.7ns per object overhead — effectively free.

You can now exclude files and directories from test discovery using glob patterns with the new --path-ignore-patterns flag or test.pathIgnorePatterns in bunfig.toml.

This is useful when your project contains submodules, vendored code, or other directories with *.test.ts files that you don't want bun test to pick up. Matched directories are pruned during scanning, so their contents are never traversed — ignoring a large directory tree is efficient.

# bunfig.toml
[test]
pathIgnorePatterns = [
"vendor/**",
"submodules/**",
"fixtures/**",
"**/test-data/**"
]

Or via the command line:

bun test --path-ignore-patterns 'vendor/**' --path-ignore-patterns 'fixtures/**'

Command-line --path-ignore-patterns flags override the bunfig.toml value entirely — the two are not merged.

Thanks to @ctjlewis and @alii for the contribution!

Fixed three bugs in UDP socket creation that caused dgram sockets to silently fail on macOS:

This affected real-world libraries like k-rpc (used by bittorrent-dht) that rely on implicit binding behavior.

import dgram from "dgram";

const socket = dgram.createSocket("udp4");

// This now correctly auto-binds on macOS, matching Node.js behavior
socket.send(Buffer.from("hello"), 0, 5, 41234, "127.0.0.1", (err) => {
if (err) console.error("send error:", err);
else console.log("sent successfully");

const addr = socket.address();
console.log("bound to:", addr); // Shows auto-assigned port
socket.close();
});

The bun_shim_impl.exe used for node_modules/.bin/* on Windows was previously hardcoded to x86_64, meaning every package binary invocation on Windows ARM64 ran under x64 emulation. The shim is now compiled natively for aarch64 when building Bun for Windows ARM64, removing the emulation overhead.

Thanks to @dylan-conway for the contribution!