Changelog

oven-sh/bun · · 20 commits

Bun tightens bundling, preload, and file handling

Major bundler fixes land for lifted CommonJS, modulepreload, and chunk splitting, alongside compile-size and file streaming bug fixes.

robobun Jarred-Sumner alii

Bundler lifts CommonJS exports more accurately (robobun696ce5a)

Bun now recognizes module.exports = require(...) patterns in unwrapped packages and lifts them into ESM exports even when side effects come first. This fixes React 19 production builds and other CommonJS-to-ESM interop cases where the bundler previously missed export lifting.

Writes through lifted CommonJS namespace objects now stick (robobun84e2bb2)

A write to the namespace object of a lifted CommonJS module now updates the underlying lifted bindings, matching Bun/Node expectations. This fixes cases like config.debug = true and React’s namespace-style assignment patterns where reads and writes had diverged.

Browser splitting gets automatic modulepreload (Jarred-Sumner7c18e0d)

Bun now emits <link rel="modulepreload"> for browser splits so import() dependency chains download in parallel instead of round-tripping one layer at a time. This is a meaningful performance win for lazy-loaded browser apps, especially deep route trees.

--min-chunk-size now folds React apps more effectively (Jarred-Sumner9c3683f)

The chunk-merging pass was expanded to cover more real-world browser dependency shapes, including lifted CommonJS modules already initialized elsewhere. That makes the option practical on React apps and avoids the static import cycle/crash it could create.

bun build --compile now errors on oversized embedded graphs (robobun1564c1e, robobun8025074)

Compile-time bundling now fails cleanly instead of producing broken executables when the embedded graph would exceed 4 GiB on Linux/FreeBSD or when Mach-O offsets overflow on macOS. This closes a correctness hole that previously surfaced as startup failures or panics.

File routes and unread file streams preserve slice bounds (robobuna28f829)

Bun.file(...).slice(...).stream() and file-serving paths now respect the original offset/length when converting unread streams back into blobs or HTTP responses. That fixes incorrect full-file reads and makes range/file route behavior consistent.

Other misc changes

  • CI lanes now run all test files on darwin PR builds.
  • Removed mitata from the root devDependencies.
  • Bumped @types/node and @lezer/cpp.
  • Fixed bun:test pretty-format handling for non-numeric size.
  • Stabilized a flaky CompressionStream HTTP sink test.
  • Fixed bun init when existing dependency fields aren’t objects.
  • Fixed auto-install logging during sleep/wait.
  • Improved entry-point handling for builtins and anonymous export-default classes.
  • Updated bundler/docs/tests around CommonJS interop, chunking, and preload behavior.