--- title: Bun v1.4.2 description: "This release fixes two regressions impacting Elysia and AsyncLocalStorage, a hang in @discordjs/ws, CMYK JPEG decoding in Bun.Image, a rare JIT crash, and a GC crash on musl." date: "2026-09-05T05:39:32.101Z" author: dylan --- This release fixes two regressions impacting Elysia and `AsyncLocalStorage`, a hang in `@discordjs/ws`, CMYK JPEG decoding in `Bun.Image`, a rare JIT crash, and a GC crash on musl. #### To install Bun {% codetabs %} ```sh#curl $ curl -fsSL https://bun.sh/install | bash ``` ```sh#npm $ npm install -g bun ``` ```sh#powershell $ powershell -c "irm bun.sh/install.ps1|iex" ``` ```sh#scoop $ scoop install bun ``` ```sh#brew $ brew tap oven-sh/bun $ brew install bun ``` ```sh#docker $ docker pull oven/bun $ docker run --rm --init --ulimit memlock=-1:-1 oven/bun ``` {% /codetabs %} #### To upgrade Bun ```sh $ bun upgrade ``` ## Fixed: `bun build` variable name collision A regression introduced in Bun v1.4.1 impacting Elysia caused `bun build` to rename a nested `var` to the same name as a `let` in the same block. Builds importing Elysia would fail to load with `SyntaxError: Cannot declare a var variable that shadows a let/const/class variable`. This has been fixed and a regression test has been added. ```js#index.js function foo () { { let exports2 = {}; var exports = exports2; } return exports; } module.exports = foo(); ``` `bun build index.js --outfile out.js` would output code containing: ```js#out.js // inside CJS module wrapper function foo() { { let exports2 = {}; var exports2 = exports2; // SyntaxError } return exports2; } module.exports = foo(); ``` The same bug could also give a `let` the name of a function parameter or `catch` binding, producing code that evaluates but computes incorrect values. ## Fixed: `AsyncLocalStorage` memory leak A regression introduced in Bun v1.4.1 caused a timer, immediate, or pending promise created inside `store.exit()` or a nested `store.run()` to keep the outer store value alive for as long as that timer or promise existed. `getStore()` still returned the correct value, so only memory usage was affected. This has been fixed. ```ts const store = new AsyncLocalStorage(); store.run(bigPerRequestContext, () => { store.exit(() => setTimeout(() => {}, 3_600_000)); // kept bigPerRequestContext alive for an hour }); ``` ## Fixed: `worker_threads` `'online'` event order A `Worker` from `node:worker_threads` didn't emit `'online'` first, causing `@discordjs/ws` to hang due to missing a worker's first message. The order now matches Node.js. ```ts import { Worker, isMainThread, parentPort } from "worker_threads"; import { once } from "events"; if (isMainThread) { const worker = new Worker(new URL(import.meta.url)); await once(worker, "online"); worker.on("message", (msg) => { console.log(msg); // never received in v1.4.1 }); } else { parentPort.postMessage("hi"); } ``` ## Fixed: `Bun.Image` decodes CMYK and YCCK JPEGs `Bun.Image` now decodes 4-component CMYK and YCCK JPEGs. Previously these failed with `Image: decode failed`. They are converted to RGB on decode, so every transform and output format works. ```ts await new Bun.Image("photo-cmyk.jpg").resize(400, 400).webp().bytes(); ``` ## Upgraded JavaScriptCore Bun v1.4.2 pulls in about 350 more upstream WebKit commits. They include `Intl` and TypedArray correctness fixes, a fix for a `Proxy` crash, and cheaper `Date` objects. ```ts new Intl.PluralRules("en").select(1n); // => "one" (was TypeError) ``` - `new Int32Array(array)` (and the other TypedArray constructors) read a stale or missing element when an element's `valueOf` mutated `array` during conversion. - `TypedArray.prototype.slice` into a `Symbol.species` view that overlaps its source on the same buffer now copies in spec order. - `Intl.DurationFormat` with `style: "digital"` no longer prints a stray `:` when `minutes` is `0` and hidden. - `Object.setPrototypeOf(handler, null)` on a `Proxy` handler that had already served a trap could crash when the handler came from a class defined inside a function called many times. ## Bugfixes - Fixed: a rare crash in long-running processes after a prototype that JIT-optimized code had cached property lookups through was garbage-collected. - Fixed: on musl (Alpine), `Array.prototype.splice`, `shift`, or shrinking `array.length` on an array of objects could crash on a GC thread or hang if it ran while the GC was marking. - Fixed: `.json()` on a `Response`, `Blob`, `Bun.file()`, or `proc.stdout` rejected invalid JSON with a generic `Failed to parse JSON` instead of the `SyntaxError` message `JSON.parse` gives, such as `JSON Parse error: Expected '}'`. - Fixed: `bun install` and `bun add` could panic with `range end index out of range` when `bun.lockb` or a cached registry manifest stored a package-name hash that didn't match the name. - Fixed: on Linux, if registering a `Bun.file().writer()` `FileSink` with epoll failed (for example `fs.epoll.max_user_watches` exhausted), its file descriptor was closed twice, which could close an unrelated descriptor that reused the number. ### Thanks to 3 contributors! - [@dylan-conway](https://github.com/dylan-conway) - [@jarred-sumner](https://github.com/jarred-sumner) - [@robobun](https://github.com/robobun)