Changelog

oven-sh/bun · Aug 31 – Sep 6, 2026 · 160 commits

Bun hardens bundling, streams, and build reproducibility

Major bundler correctness fixes, better stream/error handling, and a reproducible source build for Bun’s core deps landed this week.

Bundler correctness got a major overhaul

Bun spent the week tightening CommonJS/ESM interop, split-chunk printing, symbol renaming, tree-shaking, and hash naming. Fixes landed for lifted CommonJS exports, namespace writes, dynamic imports, re-exported namespaces, hoisted-var collisions, and #__PURE__ comment parsing, plus automatic modulepreload for browser splits and safer [hash] collision handling. These changes close several real production breakages in React apps, split bundles, and mixed module graphs.

Streams, fetch, and subprocess I/O are much more robust

A cluster of runtime fixes made aborted or failing streams clean up correctly instead of hanging or leaking. Bun.serve now cancels unread bodies on abort/HEAD and releases streaming bodies during finalization, file streams settle on error, brotli/zstd fetch decoders fully drain flushed output, and subprocess stdio errors now propagate instead of disappearing. Bun also fixed TLS force-close behavior, worker message delivery semantics, and several bun test --parallel failure modes.

Builds and installs became safer and more reproducible

Bun now builds JavaScriptCore, ICU, and related WebKit components from source in its normal graph by default, with prebuilt WebKit still opt-in. Compile-time bundling now fails cleanly when embedded graphs exceed platform limits, while install/prune work improved hardlink safety, workspace linking consistency, and mixed node_modules layout handling. The week also included lockfile corruption fixes and better handling for self-contained workspaces.

Compatibility and platform gaps were closed

HTTP/2 picked up more Node-compatible behavior around session shutdown, idle connection cleanup, flow control, and headers. DNS got better rrtype support and error mapping, macOS launch-time DNS fallback was hardened, AsyncLocalStorage was reworked for correctness and lower overhead, and NAPI finalizer timing was brought closer to Node. Bun.Image also expanded image format support with HEIC and CMYK/YCCK JPEG decoding.

Other misc changes

  • util.parseEnv() numeric keys now behave like real indexed properties
  • Bun.inspect/console.log property dedup became linear-time
  • bun run --filter now shows full output by default
  • CSS parser updated for newer pseudo-elements
  • Various docs, CI, build-system, and test-coverage updates