Bun v1.3.9

Bun v1.3.9 introduces new `bun run --parallel` and `bun run --sequential` commands that allow running multiple package.json scripts concurrently or sequentially with colored, prefixed output, including full integration with `--filter` and `--workspaces` for monorepo support. The update also fixes HTTP/2 connection upgrades via `net.Server`, and adds `Symbol.dispose` support to `mock()` and `spyOn()` in `bun:test`, enabling automatic mock restoration using the `using` keyword.

To install Bun 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 To upgrade Bun bun upgrade bun run --parallel and bun run --sequential Run multiple package.json scripts concurrently or sequentially with Foreman-style prefixed output. Includes full --filter and --workspaces integration for running scripts in parallel or sequential across workspace packages. Run "build" and "test" concurrently from the current package.json bun run --parallel build test Run "build" and "test" sequentially with prefixed output bun run --sequential build test Glob-matched script names bun run --parallel "build: " Run "build" in all workspace packages concurrently bun run --parallel --filter ' ' build Run "build" in all workspace packages sequentially bun run --sequential --workspaces build Multiple scripts across all packages bun run --parallel --filter ' ' build lint test Continue running even if one package fails bun run --parallel --no-exit-on-error --filter ' ' test Skip packages missing the script bun run --parallel --workspaces --if-present build Each line of output is prefixed with a colored, padded label so you can tell which script produced it: build | compiling... test | running suite... lint | checking files... When combined with --filter or --workspaces , labels include the package name: pkg-a:build | compiling... pkg-b:build | compiling... --parallel starts all scripts immediately with interleaved, prefixed output. --sequential runs scripts one at a time in order. By default, a failure in any script kills all remaining scripts — use --no-exit-on-error to let them all finish. Pre/post scripts prebuild /postbuild are automatically grouped with their main script and run in the correct dependency order within each group. How is this different from --filter? bun --filter="pkg" <script respects dependency order. It doesn't start a script until all it's dependendents are also run. This can be an issue when using long-lived watch-like scripts. --parallel and --sequential do not respect dependency order so they won't wait. HTTP/2 Connection Upgrades via net.Server The net.Server → Http2SecureServer connection upgrade pattern now works correctly. This pattern is used by libraries like http2-wrapper, crawlee, and custom HTTP/2 proxy servers that accept raw TCP connections on a net.Server and forward them to an Http2SecureServer via h2Server.emit 'connection', rawSocket . import { createServer } from "node:net"; import { createSecureServer } from "node:http2"; import { readFileSync } from "node:fs"; const h2Server = createSecureServer { key: readFileSync "key.pem" , cert: readFileSync "cert.pem" , } ; h2Server.on "stream", stream, headers = { stream.respond { ":status": 200 } ; stream.end "Hello over HTTP/2 " ; } ; const netServer = createServer rawSocket = { // Forward the raw TCP connection to the HTTP/2 server h2Server.emit "connection", rawSocket ; } ; netServer.listen 8443 ; Symbol.dispose support for mock and spyOn mock and spyOn now implement Symbol.dispose , enabling the using keyword to automatically restore mocks when they go out of scope. This eliminates the need to manually call mockRestore or rely on afterEach cleanup. import { spyOn, expect, test } from "bun:test"; test "auto-restores spy", = { const obj = { method: = "original" }; { using spy = spyOn obj, "method" .mockReturnValue "mocked" ; expect obj.method .toBe "mocked" ; } // automatically restored when spy leaves scope expect obj.method .toBe "original" ; } ; Symbol.dispose is aliased to mockRestore , so it works with both spyOn and mock : import { mock } from "bun:test"; const fn = mock = "original" ; fn ; expect fn .toHaveBeenCalledTimes 1 ; fn Symbol.dispose ; // same as fn.mockRestore expect fn .toHaveBeenCalledTimes 0 ; NO PROXY now respected for explicit proxy options Previously, setting NO PROXY only worked when the proxy was auto-detected from http proxy /HTTP PROXY environment variables. If you explicitly passed a proxy option to fetch or new WebSocket , the NO PROXY environment variable was ignored. Now, NO PROXY is always checked — even when a proxy is explicitly provided via the proxy option. // NO PROXY=localhost // Previously, this would still use the proxy. Now it correctly bypasses it. await fetch "http://localhost:3000/api", { proxy: "http://my-proxy:8080", } ; // Same fix applies to WebSocket const ws = new WebSocket "ws://localhost:3000/ws", { proxy: "http://my-proxy:8080", } ; --cpu-prof-interval flag Bun now supports the --cpu-prof-interval flag to configure the CPU profiler's sampling interval in microseconds, matching Node.js's flag of the same name. The default interval is 1000μs 1ms . Sample every 500μs for higher resolution profiling bun --cpu-prof --cpu-prof-interval 500 index.js If used without --cpu-prof or --cpu-prof-md , Bun will emit a warning. ESM bytecode in --compile Using --bytecode with --format=esm is now supported. Previously, this was unsupported due to missing functionality in JavaScriptCore and now it's fully supported. When --bytecode is used without an explicit --format , it continues to default to CommonJS. In a future version of Bun, we may change that default to ESM to make the behavior more consistent. Thanks to @alistair Fixed: Illegal instruction SIGILL crashes on ARMv8.0 aarch64 CPUs Fixed crashes on older ARM64 processors Cortex-A53, Raspberry Pi 4, AWS a1 instances caused by mimalloc emitting LSE atomic instructions that require ARMv8.1 or later. Bun now correctly targets ARMv8.0 on Linux aarch64, using outline atomics for runtime dispatch. Faster Markdown-to-HTML rendering Bun.Markdown now uses SIMD-accelerated scanning to find characters that need HTML escaping & , < , , " , resulting in 3-15% faster Markdown-to-HTML rendering throughput. Larger documents with fewer special characters see the biggest gains. Thanks to @billywhizz for the contribution Faster Bun.markdown.react Cached frequently-used HTML tag strings div , p , h1 -h6 , etc. in the React renderer for Bun.markdown.react , avoiding repeated string allocations on every element creation. String object count reduced by 40% and heap size reduced by 6% for a typical render. Faster AbortSignal.abort with no listeners AbortSignal.abort now skips creating and dispatching an Event object when there are no registered listeners, avoiding unnecessary object allocation and dispatch overhead. This results in a ~6% improvement in micro-benchmarks ~16ms saved per 1M calls . Thanks to @sosukesuzuki for the contribution JavaScriptCore upgrade RegExp SIMD Acceleration Regular expressions got a major performance boost with a new SIMD-accelerated prefix search, inspired by V8's approach. When a regex has alternatives with known leading characters e.g., /aaaa|bbbb/ , JSC now uses SIMD instructions to scan 16 bytes at a time, rapidly rejecting non-matching positions before falling back to scalar matching. This is implemented for both ARM64 using TBL2 and x86 64 using PTEST , so all platforms benefit. The x86 64 codegen also gained new constant materialization primitives move128ToVector , move64ToDouble , move32ToFloat using broadcast and shuffle instructions, which are necessary for the SIMD regex paths and future SIMD optimizations. 579b96614b75 — SIMD fast prefix search for RegExp ARM64 b7ed3dae4a6a — SIMD fast prefix search for RegExp x86 64 aa596dded063 — x86 64 constant materialization for SIMD masks RegExp JIT: Fixed-Count Parentheses Non-capturing parenthesized subpatterns with fixed-count quantifiers like ?:abc {3} previously fell back to the slower Yarr interpreter. They are now JIT-compiled using a counter-based loop, yielding a ~3.9x speedup on affected patterns. A follow-up patch also added JIT support for fixed-count subpatterns with capture groups e.g., / a+ {2}b/ , correctly saving and restoring capture state across iterations. ac63cc259d74 — JIT support for non-capturing fixed-count parentheses ~3.9x faster c8b66aa0832b — JIT support for fixed-count subpatterns with captures String startsWith Optimized in DFG/FTL String.prototype.startsWith is now an intrinsic in the DFG and FTL JIT tiers, with constant folding support when both the string and search term are known at compile time. Set size and Map size Optimized in DFG/FTL and Inline Caches The .size getter on Set and Map is now handled as an intrinsic in the DFG/FTL tiers and inline caches, eliminating the overhead of a generic getter call. String trim Optimized String.prototype.trim , trimStart , and trimEnd now use direct pointer access via span8 /span16 instead of indirect str i character access, avoiding repeated bounds checking. Object.defineProperty Handled in DFG/FTL Object.defineProperty is now recognized as an intrinsic in the DFG and FTL JIT tiers. While this patch alone doesn't change benchmark numbers, it lays the groundwork for future optimizations that can specialize based on descriptor shape. String.prototype.replace Returns Ropes When using "string".replace "search", "replacement" with string arguments, JSC now constructs a rope lazy concatenation instead of eagerly copying the entire result. This avoids unnecessary allocations for the common case where the result is only used briefly. This aligns with V8's behavior. Bugfixes Node.js compatibility improvements - Fixed: existsSync '.' ,statSync '.' , and othernode:fs operations incorrectly failing on Windows due to'.' being normalized to an empty string instead of the current directory. - Fixed: Function.prototype.toString whitespace now matches V8/Node.js - Fixed 3 rare crashes in node:http2 Bun APIs - Fixed: Bun.stringWidth incorrectly reporting Thai SARA AA U+0E32 , SARA AM U+0E33 , and their Lao equivalents U+0EB2 ,U+0EB3 as zero-width characters instead of width 1. These are spacing vowels, not combining marks, so common Thai words likeคำ now correctly return a width of 2 instead of 1. Web APIs - Fixed: a crash that could occur in the WebSocket client when usingbinaryType = "blob" and receiving"data" events when no event listener attached. - Fixed: Sequential HTTP requests with proxy-style absolute URLs e.g. GET http://example.com/path HTTP/1.1 hanging on the 2nd+ request when using keep-alive connections. This affected HTTP proxy servers built with Bun, which could only handle one request per connection. - Fixed: A security issue in the HTTP server chunked encoding parser that could lead to request smuggling. TypeScript types - Fixed: Bun.Build.CompileTarget TypeScript type was missing SIMD variants likebun-linux-x64-modern , causing type errors when cross-compiling with specific architecture targets. - Fixed: Missing bun-linux-x64-baseline andbun-linux-x64-modern compile target types in TypeScript definitions, which caused type errors when usingBun.build with these valid targets. - Fixed: Socket.reload TypeScript types now correctly expect{ socket: handler } to match runtime behavior, which requires the handler to be wrapped in asocket property.