Bun v1.2.22

Bun v1.2.22 introduces several key improvements, including async stack traces that now show the full asynchronous execution path for easier debugging, and a new fast path that makes `postMessage` and `structuredClone` up to 240x faster for simple objects containing only primitive values. The update also adds `Bun.YAML.stringify` for converting JavaScript objects to YAML, fixes support for interactive TTYs after stdin closes, and improves the MySQL adapter for Bun.SQL by adding `affectedRows` and `lastInsertRowid` properties.

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 Async Stack Traces async-stack-traces Bun's stack traces now include asynchronous call frames, making it significantly easier to debug code using async / await . Previously, these frames were omitted, leading to incomplete stack traces. Now, you'll see the full asynchronous execution path leading to an error. async function foo { return await bar ; } async function bar { return await baz ; } async function baz { await 1; // ensure it's a real async function throw new Error "oops" ; } try { await foo ; } catch e { console.log e ; } This now outputs: ❯ bun async.js 6 | return await baz ; 7 | } 8 | 9 | async function baz { 10 | await 1; // ensure it's a real async function 11 | throw new Error "oops" ; ^ error: oops at baz async.js:11:13 at async bar async.js:6:16 at async foo async.js:2:16 Previously, it would output: ❯ bun-1.2.21 async.js 6 | return await baz ; 7 | } 8 | 9 | async function baz { 10 | await 1; // ensure it's a real async function 11 | throw new Error "oops" ; ^ error: oops at baz async.js:11:9 Additionally, a bug that could cause stack traces printed to the console to be missing frames after accessing error.stack has been fixed. And a bug with the error stack for Error subclases has been fixed. In the next version of Bun & Safari — Bun @bunjavascript Error subclasses show where the error was thrown as the 1st frame instead of the subclass' constructor, thanks to @ sosukesuzuki pic.twitter.com/NC8Ex9DC3K September 1, 2025 Huge thanks to @sosukesuzuki for implementing this in JavaScriptCore 240x faster 240x-faster-postmessage-and-structuredclone-for-simple-objects postMessage and structuredClone for simple objects postMessage and structuredClone for simple objectsA new fast path has been added for postMessage and structuredClone when dealing with "simple" objects. This optimization applies to plain JavaScript objects that contain only primitive values like strings, numbers, booleans, null , and undefined . In the next version of Bun — Jarred Sumner @jarredsumner postMessage object gets up to 200x faster for objects with strings or primitive values. pic.twitter.com/Z4Nrj4HtJL August 31, 2025 Bun.YAML.stringify Bun.YAML.stringify In the next version of Bun — Bun @bunjavascript Bun.YAML.stringify converts JavaScript objects into YAML pic.twitter.com/ioaSb07EPX August 27, 2025 Support for interactive TTYs after support-for-interactive-ttys-after-stdin-closes stdin closes stdin closesA common pattern for TUI Terminal User Interface applications is to first process data piped from stdin , and then open /dev/tty to start an interactive session. This pattern was previously broken in Bun, causing an ESPIPE error when reading from the TTY stream. This has been fixed by correctly handling file streams for character devices. Additionally, tty.ReadStream now supports .ref and .unref for parity with Node.js, allowing for better control over the event loop in TUI applications. This resolves a long-standing bug affecting many interactive CLI tools. js import { createReadStream } from "fs"; import { stdin, stdout } from "process"; // 1. Process any data piped from stdin for await const chunk of stdin { stdout.write Piped data: ${chunk} ; } // 2. After stdin closes, open /dev/tty for interactive input stdout.write "stdin closed. Now accepting interactive input type 'exit' to quit :\n" ; const tty = createReadStream "/dev/tty" ; for await const chunk of tty { const line = chunk.toString .trim ; stdout.write You typed: "${line}"\n ; if line === "exit" { tty.destroy ; } } To run: echo "Initial data" | bun script.js Bun.SQL improvements bun-sql-improvements MySQL Adapter mysql-adapter In Bun v1.2.21, we introduced MySQL & SQLite adapters for Bun.SQL . This release includes several improvements to the MySQL adapter. affectedRows and lastInsertRowid affectedRows and lastInsertRowid properties are now returned by the MySQL driver. affectedRows contains the number of rows changed by the query, and lastInsertRowid contains the ID of the last inserted row. This brings the MySQL driver's API closer to Bun.SQL . js import { sql } from "bun"; // For INSERT queries const insertResult = await sql INSERT INTO users name VALUES 'John Doe' ; ; console.log insertResult.lastInsertRowid ; // e.g., 1 console.log insertResult.affectedRows ; // 1 // For UPDATE queries const updateResult = await sql UPDATE users SET name = 'Jane Doe' WHERE id = 1; ; console.log updateResult.affectedRows ; // 1 Better column type handling Thanks to community feedback, we've made the following improvements to MySQL driver's column type handling: | MySQL Type | JavaScript Type | Notes | |---|---|---| | INT, TINYINT, MEDIUMINT | number | Within safe integer range | | BIT 1 | boolean | Previously: TINYINT columns were incorrectly parsed as booleans instead of numbers. BIT 1 columns were incorrectly parsed as numbers instead of booleans. BIT N columns where N 1 were incorrectly parsed as Buffer s instead of numbers, but only when the binary protocol was used. TLS Support Bun.SQL now supports connecting to MySQL databases over a TLS/SSL connection. This is done by passing a tls option to the Bun.SQL constructor, matching the behavior of the PostgreSQL adapter and other Bun APIs. mysql native password authentication Bun.SQL now correctly handles mysql native password authentication and authentication switching, improving compatibility with a wider range of MySQL servers. PostgreSQL improvements postgresql-improvements - Fixed: A bug in Bun.SQL 's Postgres driver where an error in a pipelined query could cause the connection to disconnect. - Fixed: In certain cases, Bun.SQL could resolve a PostgreSQL query's Promise before the server reported being ready. - Fixed: Bun.SQL now correctly decodes TIME and TIMETZ columns from PostgreSQL when using the binary protocol. Bundler & minifier bundler-minifier In the next version of Bun — Bun @bunjavascript Bun's JavaScript transpiler & minifier gets slightly smarter pic.twitter.com/W84u1C9Q7a September 4, 2025 Minifier optimizes minifier-optimizes-new-expressions-for-smaller-bundles new expressions for smaller bundles new expressions for smaller bundlesBun's JavaScript minifier now implements several new optimizations for built-in constructors, resulting in smaller bundle sizes. When constructing built-in objects like Object , Array , or Error , the new keyword is often optional and has no effect on the runtime behavior. Bun now automatically removes the new keyword or replaces the entire expression with a more compact literal form, such as converting new Object to {} . This optimization applies to new Object , new Array , new Error and its subtypes , and new Function . js -const obj=new Object ; +const obj={}; -const arr=new Array 1, 2, 3 ; +const arr= 1,2,3 ; -const err=new Error "Something went wrong" ; +const err=Error "Something went wrong" ; Thanks to @dylan-conway for the contribution typeof undefined checks are now minified typeof undefined checks are now minifiedBun's minifier now optimizes typeof checks for "undefined" . This common optimization, also used by tools like esbuild, reduces bundle size by replacing string comparisons with shorter character comparisons. This change also improves dead code elimination for code guarded by these checks. // Input console.log typeof x === "undefined" ; console.log typeof x == "undefined" ; // Minified output console.log typeof x "u" ; console.log typeof x < "u" ; Thanks to @Jarred-Sumner and @dylan-conway for this change onEnd hook for bundler plugins onEnd hook for bundler plugins Bun.build now supports the onEnd hook in plugins, aligning its plugin API closer to esbuild. This hook is triggered after a build is complete—whether it succeeds or fails—and provides access to the BuildOutput object. This is useful for post-processing, cleanup, or sending notifications. await Bun.build { entrypoints: "./index.ts" , outdir: "./out", plugins: { name: "onEnd example", setup build { build.onEnd result = { if result.success { console.log ✅ Build succeeded with ${result.outputs.length} outputs , ; } else { console.error ❌ Build failed with ${result.logs.length} errors ; } } ; }, }, , } ; Thanks to @alii for the contribution jsxSideEffects option jsxSideEffects optionBy default, Bun's bundler treats JSX as "pure", meaning it can be removed if its return value is unused. This process, known as dead code elimination, can cause problems when a component has side effects that need to be preserved. A new option, jsxSideEffects , has been introduced to prevent this. When set to true , Bun will no longer mark JSX as pure, ensuring that components with side effects are always included in the final bundle. You can enable this feature in your tsconfig.json or by using a command-line flag. // tsconfig.json { "compilerOptions": { "jsxSideEffects": true } } This ensures that code with side effects, like the example below, behaves as expected. js // component.jsx let counter = 0; function MyComponent { counter++; // This side effect will now be preserved return <div Hello</div ; } // index.jsx <MyComponent / ; console.log counter ; // Reliably logs 1 Unused function and class names are now removed during minification unused-function-and-class-names-are-now-removed-during-minification Bun's bundler now removes unused function and class expression names when minifying --minify-syntax . This matches esbuild's behavior and results in smaller bundle sizes. A new --keep-names flag has been added to preserve these names, which can be useful for debugging or for libraries that rely on Function.prototype.name . js // input.js const myFunc = function myInternalName { // "myInternalName" is not used anywhere }; const myClass = class MyInternalClass { // "MyInternalClass" is not used anywhere }; // After bun build --minify ./input.js : // // const myFunc = function {}; // const myClass = class {}; // To preserve the names, use bun build --minify --keep-names // or keepNames: true in your build configuration. Thanks to @dylan-conway for the contribution Monitor event loop delay with monitor-event-loop-delay-with-perf-hooks-monitoreventloopdelay perf hooks.monitorEventLoopDelay perf hooks.monitorEventLoopDelay Bun now implements the perf hooks.monitorEventLoopDelay API for Node.js compatibility. This function creates and returns an IntervalHistogram object that samples the event loop delay in nanoseconds. You can use it to diagnose performance issues and understand your application's responsiveness. js import { monitorEventLoopDelay } from "perf hooks"; const histogram = monitorEventLoopDelay { resolution: 20 } ; histogram.enable ; // Introduce a delay await Bun.sleep 100 ; histogram.disable ; console.log "Event Loop Delay ns :" ; console.log "Min:", histogram.min ; console.log "Max:", histogram.max ; console.log "Mean:", histogram.mean ; console.log "50th Percentile:", histogram.percentile 50 ; console.log "99th Percentile:", histogram.percentile 99 ; // Reset for next measurement histogram.reset ; http.Server.prototype.closeIdleConnections is now implemented http.Server.prototype.closeIdleConnections is now implementedThe server.closeIdleConnections method from Node.js's http module is now implemented. This method immediately closes all sockets that are not currently handling a request, which is useful for gracefully shutting down an HTTP server without waiting for idle keep-alive connections to time out. js import { createServer } from "http"; const server = createServer req, res = { res.end "Hello, World " ; } ; server.listen 3000, = { console.log "Server listening on port 3000" ; // On a shutdown signal e.g. SIGINT process.on "SIGINT", = { console.log "Closing server..." ; // Stop accepting new connections server.close err = { if err { console.error err ; process.exit 1 ; } console.log "Server closed." ; } ; // Forcefully close any idle keep-alive connections // This allows the server.close callback to fire sooner. server.closeIdleConnections ; } ; } ; bun run now supports --workspaces bun run now supports --workspaces In the next version of Bun — Bun @bunjavascript The --workspaces flag in bun run runs the package.json script in each workspace package pic.twitter.com/sXJFwhnx79 September 7, 2025 Thanks to @dylan-conway for the contribution RFC 6455 compliant WebSocket client subprotocol negotiation rfc-6455-compliant-websocket-client-subprotocol-negotiation Bun's WebSocket client now correctly implements subprotocol negotiation as specified in RFC 6455. When you instantiate a new WebSocket with an array of desired subprotocols, Bun will send them in the Sec-WebSocket-Protocol header. The server can then select one of these protocols to use for the connection. Bun correctly validates the server's choice and makes the selected protocol available on the ws.protocol property. If the server responds with an invalid protocol, or doesn't select a protocol when one is required, the connection is now correctly rejected. This fixes a long-standing compatibility issue with popular libraries like ws and obs-websocket-js . // server which already worked fine : Bun.serve { port: 3000, fetch req, server { // Client is requesting "chat" and "superchat" protocols. // We'll select "chat". const success = server.upgrade req, { headers: { "Sec-WebSocket-Protocol": "chat", }, } ; return success ? undefined : new Response "Upgrade failed", { status: 500 } ; }, websocket: { open ws { console.log Server: new connection with protocol "${ws.protocol}" ; }, }, } ; // Client code: const ws = new WebSocket "ws://localhost:3000", "chat", "superchat" ; ws.onopen = = { // ws.protocol is now correctly set to the protocol // selected by the server. // Before, this would be an empty string. console.log Client: connected with protocol "${ws.protocol}" ; // "chat" ws.close ; }; Override override-host-and-other-headers-in-new-websocket Host and other headers in new WebSocket Host and other headers in new WebSocket You can now override special WebSocket headers like Host , Sec-WebSocket-Key , and Sec-WebSocket-Protocol when creating a new client-side WebSocket connection. This is done by passing a headers object to the WebSocket constructor. This is useful for advanced use-cases like connecting through proxies that require a specific Host header, testing servers with specific keys, or implementing custom subprotocol negotiation. Bun will automatically handle generating required WebSocket headers if they are not provided. js // Bun now supports overriding special headers in the WebSocket client const ws = new WebSocket "ws://localhost:8080", { headers: { "Host": "custom-host.example.com", "Sec-WebSocket-Key": "dGhlIHNhbXBsZSBub25jZQ==", // Must be a valid base64-encoded 16-byte key "Sec-WebSocket-Protocol": "chat, superchat", // This already worked: "X-Custom-Header": "MyValue", }, } ; Connect to specific Redis databases with connect-to-specific-redis-databases-with-bun-redisclient Bun.RedisClient Bun.RedisClient Bun's built-in Redis client, Bun.RedisClient , now supports specifying a database number directly in the connection URL, aligning with the standard Redis URI scheme. You can append /db-number to your connection string to connect to a specific database without manually sending a SELECT command. js import { RedisClient } from "bun"; // Connect to database 2 const client = new RedisClient "redis://localhost:6379/2" ; // Set a key in DB 2 await client.set "foo", "bar" ; console.log await client.get "foo" ; // "bar" // Connect to the default database 0 const defaultClient = new RedisClient "redis://localhost:6379/0" ; // The key "foo" will not be found in DB 0 console.log await defaultClient.get "foo" ; // null Thanks to @HeyItsBATMAN for the contribution Bun.redis now supports hget Bun.redis now supports hget Bun's built-in Redis client now supports the HGET command. This provides a more ergonomic and performant way to retrieve a single field from a Redis hash, returning the value directly instead of a single-element array like hmget . For single-field lookups, hget is approximately 2x faster than hmget . js import { redis } from "bun"; // Old way: returns an array const value = await redis.hmget "my-hash", "my-field" ; // New way: returns the value directly const value = await redis.hget "my-hash", "my-field" ; Faster number handling in Bun's APIs faster-number-handling-in-bun-s-apis Bun's internal APIs that return numbers, such as fs.statSync , performance.now , and process.memoryUsage , now use a more efficient number representation when the value is a whole number. Previously, these values were always represented as double-precision floating-point numbers. Now, they can be represented as tagged 32-bit integers, which makes subsequent arithmetic operations on these values significantly faster in JavaScriptCore. // Bun's APIs now return numbers in a more efficient format when possible. // Operations like this can be faster. const stats = fs.statSync file ; const size = stats.size; // This is now a tagged integer if it fits. Node.js compatibility improvements: node-js-compatibility-improvements - Fixed: A RangeError exception in child process.spawnSync when the stdio option was configured with process.stderr or process.stdout . This unblocks usage of tools like the AWS CDK. - Fixed: A bug where socket.write from node:net would incorrectly throw an exception when passed a Uint8Array . Now it allows passing Uint8Array s, matching Node.js behavior. - Fixed: A bug where crypto.verify would throw an error when a null or undefined algorithm was passed for an RSA key. It now correctly defaults to "SHA256" to match Node.js behavior. - Fixed a bug where the N-API function napi strict equals incorrectly used Object.is semantics instead of the === operator. This improves compatibility with native modules that rely on strict equality checks, such as NaN == NaN . - Fixed a crash in the N-API function napi call function that could occur when the recv the this value argument was a null pointer. - Fixed napi create array with length to correctly handle negative or oversized lengths, matching Node.js's behavior. - Fixed: util.promisify http2.connect now resolves correctly, improving Node.js compatibility for the http2 module. - Fixed: In child process , the stdin , stdout , stderr , and stdio properties are now enumerable to match Node.js behavior. This fixes compatibility with libraries like tinyspawn and youtube-dl-exec that use Object.assign on the child process object. - Fixed: Request body streaming when using node-fetch in Bun now works correctly, preventing large request bodies from being fully buffered in memory. - Fixed: A bug where Buffer.from string, 'utf-16le' produced incorrect output in rare cases. This improves Node.js compatibility. - Fixed: an incorrect assertion failure in N-API when napi reference unref is called during garbage collection. This improves compatibility with Node.js and fixes crashes in packages like rolldown-vite . - Fixed: process.versions.llhttp was missing, which improves Node.js compatibility. - Fixed: module. compile is now correctly assigned to require 'module' .prototype. compile . - Fixed: A noisy, un-actionable warning for async hooks is no longer printed to the console by default, especially when using React or Next.js. - Fixed: crypto.randomInt was not calling the callback. Now it does. - Fixed: new Buffer.isAscii string now correctly checks for ASCII; it was previously using the isUtf8 implementation by mistake. This did not impact Buffer.isAscii string , only new Buffer.isAscii string , which you probably shouldn't use anyway. - Improved: error message in Buffer.concat when concatenating buffers larger than 4GB. A RangeError is now thrown with a descriptive message. Bundler & minifier improvements: bundler-minifier-improvements - Fixed: In Bun.build , the onResolve and onLoad plugin hooks now correctly run for entrypoint files, matching esbuild's behavior. Thanks to @dylan-conway - Fixed: Runtime plugins using onResolve now correctly resolve dynamic import calls, which previously could fail with an ENOENT error. Thanks to @dylan-conway - Fixed: Bun.build now throws an AggregateError by default on build failures. To revert to the old behavior, set { throw: false } and inspect the success property on the returned BuildOutput . Thanks to @dylan-conway - Fixed: A bug where standalone binaries created with bun --compile would incorrectly include the executable's name as an extra argument in process.argv . This could cause argument parsing libraries like node:util.parseArgs to fail. - Fixed: An assertion failure in bun build that could occur when using the --compile and --bytecode flags together. - Fixed: Bundler plugins can now intercept entry points with onResolve , fixing a bug that prevented the creation of virtual entry points. - Fixed: A bug where build.module in a Bun plugin would fail to parse TypeScript syntax when using loader: 'ts' . - Fixed: Bun.build was missing the splitting property in its TypeScript types. - Fixed: On Windows, single-file executables created with bun build --compile no longer have an incorrect "Original Filename" metadata field set to "bun.exe". - Fixed: A regression on Windows where bun build --compile would fail when using embedded resources or a relative path for --outfile . - Fixed: a memory leak in Bun.plugin where onLoad filters using regular expressions would not be garbage collected, causing memory usage to grow over multiple builds. - Fixed: A bug causing non-deterministic module resolution for packages that ship both CommonJS and ES Module versions. This could lead to inconsistent builds and "dual package hazard" errors. - Fixed: an error when parsing linear-gradient with turn angle units. - Fixed: A bug where certain modules using top-level await were missing a async keyword, causing a runtime error. - Fixed: A bug where banner option with format: "cjs" and target: "bun" could produce a syntax error if banner contained a shebang. JavaScript runtime improvements: javascript-runtime-improvements Bun.YAML.parse now accepts Buffer , ArrayBuffer , TypedArray s, DataView , and Blob as input.- Fixed: Bun.Cookie.isExpired now correctly returns true for cookies with an Expires date set to the Unix epoch Thu, 01 Jan 1970 00:00:00 GMT . - Fixed: an exception in crypto.subtle.importKey when importing RSA private keys with Chinese Remainder Theorem parameters. This resolves a compatibility issue with the jose JWT library. - Fixed: a bug that caused fetch requests with large bodies to fail with an ECONNRESET error when using an HTTP proxy for an HTTPS connection. - Fixed: Errors thrown inside HTMLRewriter handlers are now correctly propagated as catchable JavaScript errors, instead of causing a native code: Exception message or a crash. - Fixed: A reliabiltiy issue in HTMLRewriter - Fixed: an assertion failure when using the BUN INSPECT CONNECT TO environment variable in a project that loads environment variables from a .env file. - Fixed: a crash when using Bun.secrets on Linux. - Fixed: fetch throwing a Decompression error: ShortRead when receiving an empty response with Content-Encoding: gzip and Transfer-Encoding: chunked . This also occurred with brotli and zstd in some cases. - Fixed: A bug where structuredClone would throw a "TypeError: Unable to deserialize data" when cloning nested objects or arrays containing a Blob or File . Additionally, the name property of File objects is now correctly preserved after cloning. - Fixed: A bug causing error stack traces to be truncated, which made debugging more difficult. - Fixed: A bug causing fetch to hang when the server responds with a 101 Switching Protocols status, which is used to upgrade a connection to a WebSocket. fetch in Bun continues to not support WebSocket connections, it now errors instead of hanging. - Fixed: new WebSocket now emits an error event before the close event when a connection handshake fails. Previously, only a close event was emitted, which was inconsistent with browser behavior. process.versions now displays semantic versions for zlib and libdeflate instead of commit hashes.- Fixed: A regression causing bun --watch to crash when a file is deleted. - Fixed: A bug where bun --watch would not correctly handle changes in swap files. Bun.SQL bugfixes: bun-sql-bugfixes - Fixed: A regression from Bun v1.2.21 impacting DATABASE URL options precedence in Bun.SQL connection string parsing. - Fixed: A potential crash in Bun.SQL when closing a MySQL or PostgreSQL database connection. Shell improvements: shell-improvements - Fixed: A shell crash when using environment variable assignments in a pipeline, such as VAR=val | command . - Fixed: A regression from Bun v1.2.21 where certain commands would trigger an assertion failure on Windows. bun install improvements: bun-install-improvements - Fixed an internal data structure in bun patch to use one-based line indexing by default. - Fixed: a panic when installing a global package with --trust if it contained dependencies that were already trusted. - Fixed: A crash that could occur during bun install when applying a malformed patch file with out-of-bounds line numbers. - Fixed: A bug where bun audit could hang indefinitely due to a cycle in the dependency graph has been resolved. - Fixed: A bug when extracting tarballs with unusual package names could produce an invalid temporary filename, particularly on Windows. TypeScript types: typescript-types - Fixed: Added missing types for AbortSignal.aborted and RegExp.escape to bun-types . - Fixed: Added missing TypeScript types for Bun.YAML.parse .