Bun v1.3.1

Bun v1.3.1 introduces significant performance improvements, including up to 2x faster builds for projects using isolated linkers or symlinks, and faster installs by removing an unnecessary sleep() call when no peer dependencies are present. The update also adds new testing features like a global `vi` object for Vitest compatibility, `--pass-with-no-tests` and `--only-failures` flags, and enhanced sourcemap support for legal comments. Additionally, the package manager now supports the `:email` field in `.npmrc` for private registries and introduces selective hoisting via `publicHoistPattern` and `hoistPattern` configurations.

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 Faster faster-bun-build bun build bun build For projects that use --linker=isolated , pnpm , or otherwise use lots of symlinks, bun build gets up to 2x faster. In the next version of Bun — Jarred Sumner @jarredsumner bun build with sourcemaps & minification enabled gets 2x faster pic.twitter.com/bjaU6YK9xV October 12, 2025 Sourcemaps for legal comments in sourcemaps-for-legal-comments-in-bun-build bun build bun build Source maps now include entries for preserved multi-line comments including CRLF line endings , ensuring legal comments in bundled output map back to their original sources for accurate debugging and tooling. import.meta in CommonJS import.meta in CommonJS bun build --format=cjs will now inline some usages of import.meta similarly to existing behavior with dirname and filename . This prevents syntax errors that could occur when transpiling files using import.meta to CommonJS, such as packages like @sentry/node . | ESM-ism | CommonJS-ism | |---|---| import.meta.url | - | import.meta.path | filename | import.meta.dirname | dirname | import.meta.file | path.basename module.filename | New in new-in-bun-test bun test bun test vi global vi global bun test now exposes Vitest's global vi including types . vi is defined in test files by default, enabling vi.fn , vi.mock , vi.spyOn , and related APIs without imports. js test "hello", = { const fn = vi.fn ; expect fn .not.toHaveBeenCalled ; fn ; expect fn .toHaveBeenCalled ; } ; This makes it a little bit easier to migrate from Vitest to bun test . bun test --pass-with-no-tests bun test --pass-with-no-tests The test runner now supports --pass-with-no-tests , which exits with code 0 when no tests are found or when active filters match no tests. This mirrors Jest and Vitest behavior and is useful in monorepos where some packages may not contain tests. Without the flag, bun test continues to exit with 1 when no tests are found. Actual test failures still exit non-zero. bun test --pass-with-no-tests bun test v1.3.1 No tests found Tests need ".test", " test ", ".spec" or " spec " in the filename ex: "MyApp.test.ts" Learn more about bun test: https://bun.com/docs/cli/test echo $? 0 Thanks to @pfg for the contribution bun test --only-failures bun test --only-failures A new --only-failures flag and test.onlyFailures option in bunfig.toml hides passing tests and prints only failures, making large suites and CI logs easier to scan. The final summary pass/skip/fail, totals is still printed. bun test --only-failures bun test v1.3.1 10 pass 0 fail Ran 1 tests across 1 file. 8.00ms Thanks to @pfg for the contribution New in bun install new-in-bun-install Faster installs when no faster-installs-when-no-peerdependencies-are-present peerDependencies are present peerDependencies are presentWe removed a sleep in Bun’s package manager It waited for peer dependencies to install, even if there were no peer dependencies to install. Thanks to @dylan-conway for fixing this :email in .npmrc :email in .npmrc Some private registries e.g., Sonatype Nexus require an email alongside username/password or token. bun install now reads and forwards the :email field from .npmrc for both default and scoped registries, enabling successful authentication in these setups. .npmrc //registry.example.com/:email=user@example.com //registry.example.com/:username=myuser //registry.example.com/: password=base64encodedpassword or with a token //registry.example.com/: authToken=xxxxxx Thanks to @dylan-conway for the contribution publicHoistPattern and hoistPattern publicHoistPattern and hoistPattern Bun now supports selective hoisting when using the isolated linker. publicHoistPattern in bunfig.toml and public-hoist-pattern in .npmrc hoists matching transitive dependencies to the root node modules so tools like ESLint and TypeScript lib augmentations can be discovered across a workspace. hoistPattern controls what gets hoisted into node modules/.bun/node modules. This makes it possible to explicitly opt-in packages such as @types/ , eslint plugins, or better-typescript-lib for global visibility in monorepos without reverting to full hoisting. install String form publicHoistPattern = "@types " Array form publicHoistPattern = "@types ", " eslint " Control internal hoisting into node modules/.bun/node modules hoistPattern = "@types ", " eslint " Equivalent to bunfig.toml, useful when sharing config across tools public-hoist-pattern =@typescript/ public-hoist-pattern = eslint FileHandle.readLines in node:fs/promises FileHandle.readLines in node:fs/promises Bun now implements Node.js’s FileHandle.readLines , enabling efficient, backpressure-aware async iteration over file lines using for-await-of. This handles empty lines and CRLF correctly and accepts the same options as createReadStream e.g., encoding . js import { open } from "node:fs/promises"; const file = await open "file.txt" ; try { for await const line of file.readLines { encoding: "utf8" } { console.log line ; } } finally { await file.close ; } Thanks to @nektro for the contribution Bundler & Transpiler bugfixes bundler-transpiler-bugfixes - Improved: Bundler CJS output incorrectly respected esModule when the importer used ESM syntax. toESM now bases isNodeMode on the importing module's syntax ESM import/export sets isNodeMode=1 , matching - Improved: bun build --no-bundle now rejects HTML entrypoints with a clear error "HTML imports are only supported when bundling" - Fixed: An assertion failure when transpiling code that evaluates string equality in constant-known expressions involving concatenated strings rope strings in rare cases. - Fixed: Bun.build with compile: true failed to apply sourcemaps including sourcemap: "inline" or true , causing stack traces to reference virtual bundled paths /$bunfs/root/ instead of original files/lines. The API now mirrors bun build --compile by emitting external sourcemaps in compile mode, restoring correct file names and line numbers in error stacks. - Fixed: bun build --bytecode could fail when code referenced import.meta.url or import.meta.dir . These now compile without errors. - Fixed: An assertion failure in bun build --production impacting Windows when react-jsxdev is present in tsconfig.json - Fixed: Incorrect memory management for error message strings in bun build --compile for single-file executables in certain cases. - Fixed: Assertion failure when encountering certain invalid async function syntax patterns. Now Bun reports an error. - Fixed: "Scope mismatch while visiting" panic when encountering TypeScript enums with function-valued members e.g. A = = {} - Fixed: A race condition when using with {type: "macro"} when executed simultaneously for the first time across multiple threads in bun build bun test bugfixes bun-test-bugfixes - Fixed: bun test could crash when formatting errors for extremely deeply nested objects bun install / bun pm bun-install-bun-pm - Fixed: bun install with --linker=isolated on macOS could fail with EXDEV Cross-device link when the project lived on a non-system APFS volume or across volumes common in workspaces/monorepos . Installs now handle cross-volume linking correctly and complete reliably. - Fixed: bun install with the isolated linker did not create symlinks for self-referencing workspace dependencies in monorepos e.g., "workspace:\ " or "workspace:." , preventing packages from resolving their own exports via node modules . These self-deps are now correctly linked. - Fixed: A determinism bug when constructing node modules/.bun/node modules under --linker=isolated , which could cause different versions to be hoisted across installs and enable unintended "phantom" dependencies across workspaces despite using --linker=isolated . - Fixed: Missing error handling when iterating directory entries in certain cases. - Fixed: bun pm pack now always includes files and directories declared via "bin" and "directories.bin" even when they are not listed in "files" , matching npm pack behavior. This prevents missing CLI binaries in published tarballs and deduplicates paths when they appear in both "bin" / "directories.bin" and "files" bunx bunx - Fixed: A panic in bunx on Windows that could occur when npm package names contained multi-byte/non-ASCII characters which npm's registry does not support . Bun.SQL / MySQL bun-sql-mysql - Fixed: Missing error handling in MySQL parameter binding when passing boxed primitives new Number ... , new Boolean ... or other non-indexable values. Bun now throws a descriptive error instructing you to use primitive numbers/booleans instead. - Fixed: MySQL TLS connections could spin a CPU core at 100% after a query sslmode=require/prefer , especially on macOS. Timers are now initialized only after connection status transitions complete, preventing runaway timeouts. - Fixed: a regression from v1.2.23 causing idle MySQL connections to keep the event loop alive. Processes now exit cleanly after queries instead of hanging Bun.RedisClient bun-redisclient - Fixed: Bun.RedisClient now validates connection URLs and throws on invalid parameters e.g., out-of-range ports instead of silently defaulting to localhost:6379 Bun.S3Client bun-s3client - Fixed: Memory leak in Bun.S3Client listObjects response parsing ETag handling that could cause unbounded memory growth when listing large buckets or repeatedly calling listObjects bun:ffi bun-ffi - Fixed: bun:ffi now surfaces actionable dlopen linking errors. When a library cannot be opened, the error includes the library path and the OS error e.g. "invalid ELF header", "No such file or directory" instead of a generic message. - Fixed: linkSymbols and CFunction now throw a clear error when a symbol definition is missing a ptr field, and an error propagation issue in linkSymbols was corrected so errors are thrown consistently. Bun Shell $ bun-shell - Fixed: a memory leak in Bun Shell command-line arguments. - Fixed: a crash that could occur when Bun Shell is garbage collected. - Fixed: Blocking I/O on macOS when writing large 1 MB outputs to pipes - Fixed: Potential assertion failure on Windows when spawning from long paths or when 8.3 short names are disabled. - Fixed: Missing error handling when monitoring shell writers on Windows WebSocket client & server websocket-client-server - Fixed: WebSocket upgrades ignored cookies set with req.cookies.set prior to server.upgrade ; the Set-Cookie header is now included in the 101 Switching Protocols response, with or without custom headers - Fixed: Incorrect handling of WebSocket client close frames could panic when the close frame payload was fragmented across multiple TCP packets. Bun now buffers fragmented close frames and processes them only when complete Node.js Compatibility node-js-compatibility - Fixed: a crash that could occur when terminating a Worker that used N-API. This impacted next build with Turbopack enabled. - Fixed: Missing libuv error codes UV ENOEXEC and UV EFTYPE are now recognized on Windows. - Fixed: The node:buffer ESM export of INSPECT MAX BYTES was incorrectly exposed as an accessor. It is now a plain number, matching Node.js semantics; reassigning buffer.INSPECT MAX BYTES does not affect the ESM named import. - Fixed: Response.json now throws a Node.js-compatible TypeError "Value is not JSON serializable" for non-serializable top-level values Symbol , Function , undefined . BigInt now throws "Do not know how to serialize a BigInt". Thank you to Martin Schwarzl of Cloudflare for reporting these bugs: - Fixed: out-of-bounds write in Buffer.prototype.writeBigInt64{LE,BE} and Buffer.prototype.writeBigUInt64{LE,BE} - Fixed: assertion failure when setting process.title with UTF‑16 characters - Fixed: missing exception handling for a ReadableStream for use by a Response.prototype.body that throws during initialization Web APIs web-apis - Fixed: a bug that could cause excessive memory growth in certain rare cases when consuming fetch response bodies chunk-by-chunk. Thank you to Martin Schwarzl of Cloudflare for also reporting the following bugs: - Fixed: URL heap size accounting could overflow, causing pathological GC behavior when handling large URLs. Memory usage is now reported accurately. - Fixed: assertion failure in URLSearchParams.prototype.toJSON involving numeric string keys - Fixed: assertion failure in Headers.prototype.append involving numeric header names YAML yaml - Fixed: Bun.YAML.parse no longer treats "..." inside double-quoted strings as a document end marker, eliminating "Unexpected document end" errors for valid quoted text e.g., internationalized strings with ellipses . - Fixed: Bun.YAML.stringify now correctly double-quotes strings that begin with YAML indicator characters or leading whitespace e.g., :, -, ?, , , {, }, , &, , , |, , ', ", %, @, , space, tab, newline , ensuring Bun.YAML.parse Bun.YAML.stringify ... round-trips without SyntaxError . Console console - Fixed: incorrect error-handling when printing Set or Map instances where a subclass overrides the size property with a non-numeric value. Thanks to Martin Schwarzl & Cloudflare for the report Hot Reload hot-reload - Fixed: On macOS, saving the entrypoint with Vim's atomic write could intermittently trigger "Module not found" during bun --hot reload; Bun now defers reload until the file is recreated and verified. Templates templates - Fixed: React templates react-app, react-shadcn, react-tailwind had dev and start scripts pointing to src/index.tsx after the entry file was renamed to src/index.ts, causing run failures. Scripts now correctly reference src/index.ts. Windows-specific windows-specific - Fixed: Hang when running package.json scripts on Windows for non-English locales. Windows environment variables and paths are now converted to "WTF-8" at startup. This fixes hangs when using PowerShell with Bun when usernames or working directories that contained non-ASCII characters. This is a regression from Bun v1.2.23. Thanks to 15 contributors thanks-to-15-contributors @alinalihassan https://github.com/alinalihassan @cirospaciari https://github.com/cirospaciari @dylan-conway https://github.com/dylan-conway @hoxyy https://github.com/hoxyy @jarred-sumner https://github.com/jarred-sumner @jsparkdev https://github.com/jsparkdev @mariusz4044 https://github.com/mariusz4044 @markovejnovic https://github.com/markovejnovic @nektro https://github.com/nektro @pfgithub https://github.com/pfgithub @riskymh https://github.com/riskymh @robobun https://github.com/robobun @shlomocode https://github.com/shlomocode @sosukesuzuki https://github.com/sosukesuzuki @taylordotfish https://github.com/taylordotfish Special thanks to Martin Schwarzl of Cloudflare for fuzzing & reporting several bugs