### Problem
The bundler's `__toESM` helper creates a new getter-wrapped proxy object
every time a CJS
module is imported. In a large app, a popular dependency like React can
be imported 600+
times — each creating a fresh object with ~44 getter properties. This
produces ~27K
unnecessary `GetterSetter` objects, ~25K closures, and ~25K
`JSLexicalEnvironment` scope
objects at startup.
Additionally, `__export` and `__exportValue` use `var`-scoped loop
variables captured by
setter closures, meaning all setters incorrectly reference the last
iterated key (a latent
bug).
### Changes
1. **`__toESM`: add WeakMap cache** — deduplicate repeated wrappings of
the same CJS
module. Two caches (one per `isNodeMode` value) to handle both import
modes correctly.
2. **Replace closures with `.bind()`** — `() => obj[key]` becomes
`__accessProp.bind(obj,
key)`. BoundFunction is cheaper than Function + JSLexicalEnvironment,
and frees the for-in
`JSPropertyNameEnumerator` from the closure scope.
3. **Fix var-scoping bug in `__export`/`__exportValue`** — setter
closures captured a
shared `var name` and would all modify the last iterated key. `.bind()`
eagerly captures
the correct key per iteration.
4. **`__toCommonJS`: `.map()` → `for..of`** — eliminates throwaway array
allocation.
5. **`__reExport`: single `getOwnPropertyNames` call** — was calling it
twice when
`secondTarget` was provided.
### Impact (measured on a ~23MB single-bundle app with 600+ React
imports)
| Metric | Before | After | Delta |
|--------|--------|-------|-------|
| **Total objects** | 745,985 | 664,001 | **-81,984 (-11%)** |
| **Heap size** | 115 MB | 111 MB | **-4 MB** |
| GetterSetter | 34,625 | 13,428 | -21,197 (-61%) |
| Function | 221,302 | 197,024 | -24,278 (-11%) |
| JSLexicalEnvironment | 70,101 | 44,633 | -25,468 (-36%) |
| Structure | 40,254 | 39,762 | -492 |
## Summary
- Implement complete lowering of TC39 stage-3 standard ES decorators
(the non-legacy variant used when tsconfig has no
`experimentalDecorators`).
- Passes all 147 esbuild decorator tests and 22 additional Bun-specific
tests (191 total, 0 failures).
- Supports method, getter, setter, field, auto-accessor, private member,
and class decorators in both statement and expression positions, with
proper evaluation order, class binding semantics, and decorator
metadata.
Fixes#4122Fixes#20206Fixes#14529Fixes#6051
## What's implemented
| Feature | Details |
|---|---|
| Method/getter/setter decorators | Static and instance, public and
private |
| Field decorators | Initializer replacement + extra initializers via
`__runInitializers` |
| Auto-accessor (`accessor` keyword) | Lowered to WeakMap storage +
getter/setter pair |
| Private member decorators | WeakMap/WeakSet lowering with
`__privateGet`/`__privateSet` |
| Class decorators | Statement and expression positions |
| Class expression decorators | Comma-expression lowering (no IIFE) |
| Decorator metadata | `Symbol.metadata` support via
`__decoratorMetadata` |
| Evaluation order | All decorator expressions + computed keys evaluated
in source order per TC39 spec |
| Class binding semantics | Separate inner/outer class name bindings
(element vs class decorator closures) |
| Static block extraction | `this` replaced with class name ref when
moved to suffix |
| Computed property keys | Pre-evaluated into temp variables for correct
ordering |
## Runtime helpers
Added to `src/runtime.js` and registered in `src/runtime.zig`:
- `__decoratorStart(base)` — creates decorator context array
- `__decorateElement(array, flags, name, decorators, target, extra)` —
applies decorators to a class element
- `__decoratorMetadata(array, target)` — sets `Symbol.metadata` on the
class
- `__runInitializers(array, flags, self, value)` — runs
initializer/extra-initializer arrays
## Test plan
- [x] `bun bd test
test/bundler/transpiler/es-decorators-esbuild.test.ts` — **147/147
pass** (esbuild's full decorator test suite)
- [x] `bun bd test test/bundler/transpiler/es-decorators.test.ts` —
**22/22 pass**
- [x] `bun bd test test/bundler/transpiler/decorators.test.ts` — **22/22
pass** (legacy decorators still work)
- [x] E2E runtime verification of method, field, accessor, class,
private, and expression decorators
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>
### What does this PR do?
Currently bundling and running projects with cyclic async module
dependencies will hang due to module promises never resolving. This PR
unblocks these projects by outputting `await Promise.all` with these
dependencies.
Before (will hang with bun, or error with unsettled top level await with
node):
```js
var __esm = (fn, res) => () => (fn && (res = fn((fn = 0))), res);
var init_mod3 = __esm(async () => {
await init_mod1();
});
var init_mod2 = __esm(async () => {
await init_mod1();
});
var init_mod1 = __esm(async () => {
await init_mod2();
await init_mod3();
});
await init_mod1();
```
After:
```js
var __esm = (fn, res) => () => (fn && (res = fn((fn = 0))), res);
var __promiseAll = Promise.all.bind(Promise);
var init_mod3 = __esm(async () => {
await init_mod1();
});
var init_mod2 = __esm(async () => {
await init_mod1();
});
var init_mod1 = __esm(async () => {
await __promiseAll([init_mod2(), init_mod3()]);
});
await init_mod1();
```
### How did you verify your code works?
Manually and tests
---------
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>
* some progess
* needs more tests
* make tests easier to debug
* get metadata for constructor arg decorators
* fix some things
* merge `emitDecoratorMetadata` option
* remove `^`
* bundler tests and get option from tsconfig earlier
* remove spaces
* fix tests
* alright now just gotta try running it
* fix a gajillion compiler errors
* even more code
* okay i fixed more errors
* wip
* Update launch.json
* Update string_builder.zig
* `fast_debug_build_mode` makes debug build 2x faster
* Update bundle_v2.zig
* more code!
* It bundles!
* Rename `Bun.Transpiler` to `Bun.Bundler`
* `import()` expressions almost work
* wip attempt to get import() expr to work
* Bundle namespace imports
* Attempt to fix the issue with import() unsuccessfully
* consider current working directory when resolving relative paths (#2313)
* consider current working directory when resolving relative paths
fixes#2298
* comment test
---------
Co-authored-by: Jarred Sumner <709451+Jarred-Sumner@users.noreply.github.com>
* support `expect().toThrow(/pattern/)` (#2314)
- fix time-zone-dependent test failure
* fix missing `Blob` error messages on Linux (#2315)
* fix & clean up tests (#2318)
- skip flaky tests when running as `root`
- use `expect().toThrow()`
- clean up temporary files after tests
* feat(tty): add some `tty.WriteStream` methods to `process.{stdout, stderr}` (#2320)
* feat(stdio): add some `tty.WriteStream` methods
* chore(builtins): add process builtin gen'd code
* Fix docker install command
* `bun test` on macOS in GitHub Actions (#2322)
* Fixes#2323
* throw invalid parameter errors in `crypto.scryptSync` (#2331)
* throw invalid parameter errors
* remove comptime, add empty buffer function
* remove error_name comptime
* Add reference documentation for bun:test (#2327)
* Reorganize tests (#2332)
* Fix html-rewriter.test.js
* fix the wrong thing being incremented in hmr example (#2334)
* Add more test harness
* Improve Benchmarking page, small fixes (#2339)
* Improve benchmarking page
* WIP
* Add typescript instructions to hot
* Document preload in Plugins. Fix loader in plugin types.
* Fix typo
* Fix links
* run prettier
* Document openInEditor
* improve `Buffer` compatibility with Node.js (#2341)
* improve `Buffer` compatibility with Node.js
* use `memmove()`
allow `encoding` to be `undefined`
* run `bun test` after macOS builds (#2343)
* "binary" is an alias of "latin1"
Fixes https://github.com/oven-sh/bun/issues/2110
* More spec compliant `Blob.prototype.type` (#2340)
* Make `Blob.prototype. type` more spec compliant
* Add a few more checks for isNumber()
* Fix `make headers`
* Safer JSValue.isString()
* More tests for blob.slice
* Make `Blob.prototype.type` more spec compliant
* Add isASCII check
* Fix types
* Fix failing type test
* Update blob.zig
* Update blob.zig
* Fix .eql check on empty values
---------
Co-authored-by: Jarred Sumner <709451+Jarred-Sumner@users.noreply.github.com>
* Fix bug in test runner
* Support `import()` expressions
* Implement `require()`
* clean up bit_set.zig slightly
* Move some things around
* misc cleanup
* Cleanup some things
* Fix a lot of stuff
* Fix `module.exports.fn = fn;` in ESM entry point
* Fix crash due when printing file
* Fix issue with class names
* Fix issue with `export default identifier`
* Update js_parser.zig
* optimization: inline single-property object acceses and arrays
* Fix undefined memory in renamed symbols list
* Handle call target
* wip
* Inline it
* Fix undefined memory issue when reclaiming blocks in ast
* Halt linking on any parse errors
* alias
* Rename `enable_bundling` to `enable_legacy_bundling`
* Workaround anonymous struct literal zig bug
* Use slower approach (without bitset) because it doesn't break after 8 symbols
* Fix incorrectly-renaming statically defined symbols
* Handle more edgecases in our bit_set fork
* Reduce number of allocations for `define`
* Do not rename unbound symbols
* Clean up dot defines a little more
* Make the generated names prettier
* Workaround runtime symbol missing issue
* Fail the build on errors
* Support export * from
* Support `--outfile`
* partially fix renaming
* fanicer symbol renaming impl
* misc, extremely revertible cleanup
* Fix up some bugs with symbol renaming
* formatting
* Update launch.json
* Parse `__PURE__` comments
* clean up simd code for pure comments
* changes to merge
* workaround runtime issue
* Fix issue with `export * as` not propagating correctly
* Make all top-level declarations `var` when bundling
* Fix missing prefix
* Fix assigning to stack copy
* Fix missing runtime symbol
* Fix bug with namespace exports
* Dramatically reduce allocations
* Update launch.json
* Add missing flags
* Update js_parser.zig
* small cleanup
* Make the export name better
* Fix unnecessary `var foo = foo`
* Implement CommonJS -> ESM conversion
* Implement module redirects
* Port esbuild bundler tests for new bundler (#2380)
* started porting esbuild tests
* clean up test names and api before moving on
* port tests using a program i wrote
* replace todo generated comment
* fix generated tests not including some files
* work on tests
* [github web editor] add define, external, inject, minifySyntax, minifyWhitespace options.
* get most of the todo comments out of the way, but expectBundled does not handle most of the cases
* continue working on esbuild tests
* use test.skip for unsupported tests
* Fixups for test runner
* Hoist imports & exports
* Fix test
* Hoist classes
* bundler test refining, 51/835
* Fix runtime require
* bundler test refining, 81/835
* bundler test refining, 93/835
* Make the test work in any timezone
* feat(expect): update toBeInstanceOf (#2396)
* feat: update instanceof binding
* fix: according to PR comments
* Rename `expectObjectTypeCount` to `expectMaxObjectTypeCount`
* Fix socket tests with connection errors (#2403)
* release pending activity with connection error handler
* unref poll_ref
* remove trailing comma
* Organize Dockerfiles for official status
* Remove test Dockerfile
* Remove old Docker workflow
* Feat(test): add toMatch (#2404)
* Fix various fetch/response/request tests (#2416)
* fix most fetch tests, skip a few
* fastGet, toValueGC, and invalid init
* bigint unreachable, range error, log process as process
* remove extra fetch_headers
* remove js_type parameter, check isObject()
* throw invalid mime type error, use enum literal
* switch back to promise rejection
* RangeError pascal case
* Fix several bugs (#2418)
* utf16 codepoint with replacement character
* Fix test failure with `TextEncoder("ascii')`
* Add missing type
* Fix Response.prototype.bodyUsed and Request.prototype.bodyUsed
* Fix bug with scrypt error not clearing
* Update server.zig
* oopsie
* 💅
* docs: Use correct url in the 'Issues' link in README header (#2420)
* Fix crash when rendering error page and the server or network is slow
* [fetch] Make the default body value `null` when unspecified
This is better aligned with the fetch spec
* Make node-net tests less flaky
* [node:net] Fix issue with `listen` callback firing before it's listening
* Always clear timers in node test harness
* Fix out of bounds access
Repro'd in Buffer tests
* Update UWS
cc @cirospaciari
* Make this test more thorough
* Hanging abort test
* 0 length body is a null stream
* Several bug fixes (#2427)
* Fix test
* Fix segfault when unexpected type is passed in `expect().toThrow`
* Fix issues with request constructor
* Don't bother cloning headers when its empty
* woops
* more tests
* fix incorrect test
* Make the fetch error messages better
* Update response.zig
* Fix test that failed on macOS
* Fix test
* Remove extra hash table lookups
* Support running dummy registry directly
cc @alexlamsl
* Update test
* Update test
* fixup
* Workaround crash in test runner
* Fixup test
* Fixup test
* Update os.test.js
---------
Co-authored-by: Jarred Sumner <709451+Jarred-Sumner@users.noreply.github.com>
* Remove usages of port numbers in tests
* Set -O2 and -fno-rtti
* Remove -g
* Prevent undefined memory access
* [bun test] Implement `--rerun-each` flag to run each test N times
* Reduce number of module scopes created
* add some extra abort checks into streams (#2430)
* add some checks to avoid UAF
* avoid multiple calls to finalize if endFromJS is called more than once
* fix no-op comment
* mark as requested_end on abort
* remove requested_end from abort
* remove unnecessary check (#2432)
* Fix bug with scoped aliased dependencies in bun install on macOS
* remove `addLog`, remove `--prominent-compile-errors`
* Finish the upgrade
* Optional chaining flag
* Implement same_target_becomes_destructuring optimization
* bundler test refining, 109/835
* Reset bindings
* Support multiple entry points
* Implement `--entry-names` flag
* Use a tempdir with a better name
* prettier
* Log file name
* Update js_parser.zig
* Mark all bun builtins as external
* Make resolve errors actually errors
* Update bundler_default.test.ts
* Fix `await import(foo)`
* WIP react server components
* Do more stuff at runtime
* ✂️
* Support automatic JSX imports
* Use a module cache for now
* Update tsconfig.base.json
* Fix ThisOutsideFunctionNotRenamed
* woopsie
* moar cpu
* clamp it
* fixup
* Add a bunch of assertions
* Bun uses automatic runtime by default
* Parse Import Attributes
* Add a note about Valgrind
* Update developing.md
* Fix up code splitting for React Server Components
* Implement client component manifest
* Fix crash with --react-server-components and no client components
* Backport 4d31e3c917
* Update launch.json
* Fix for latest zig
* Workaround bug with ?[]const string
Occasionally saw alignment errors in this code
Workaround https://github.com/ziglang/zig/issues/15085
related: https://github.com/ziglang/zig/pull/15089
* switch to regular slice
* Avoid initializing named_imports and named_exports as undefined
* Reduce usages of `undefined`
* Add more assertions
* --watch wip
* Update javascript.zig
* Possibly fix the race condition
* Faster `do`
* bump allocator
* Reduce the size of `Symbol` slightly
* Alphabetically sort runtime import symbols, for determinism
* Prepare for code splitting
* handle overlapping stdout
* pure
* clean up some things
* Fix bug with `$$typeof`
* Address CommonJS -> ESM hoisting bug
* Support `"use server"` in manifest
* Implement `"use server"`
* Fix importing bun builtins when bundling
* Make `commonjs_to_esm` a feature flag, fix some splitting bugs
* ✂️
* fixme remove this
* Fix crash in longestCommonPath
* Chunking! Just need to do import paths now.
* Import paths work...now trying to figure out how to make runtime symbols work
* add workaround
* Replace `bun bun` with `bun build`
* Fix crash with dual package hazard
* Fix many CommonJS <> ESM interop bugs
* Support package.json `"sideEffects"`
also skip loading unnecessary package.json data in `bun run`
* add a not good --watch implementation
* bundler test refining, 140/831
* remove accidentally committed file
* do not return status code 1 on successful bundles
* bundler test refining, 159/830
* pass exit code to exitOrWatch
* clean up help menu
-remove two spaces to line up bun build
-moved all <r> tags to the end of the text they are colorizing
-moved other colors to the start of the text they colorize
-removed unneeded <r> tags, keeping only one at the start of the block
* importstar is fully ported
* wip
* you can run code in this branch now
* Disable this transform
* organize and document bundler tests
* Fix double import
* Fix sloppy mode function declarations
* Disable our CommonJS transform for now
* add `assertNotPresent` to make splitting cases easier
* Bump!
* Update bun.d.ts
* use import.meta.require in runtime code
* Disable this again
* Fix dirname
* Fix ESM -> CJS wrapper
* 💅
---------
Co-authored-by: Jarred Sumner <709451+Jarred-Sumner@users.noreply.github.com>
Co-authored-by: Alex Lam S.L <alexlamsl@gmail.com>
Co-authored-by: Derrick Farris <mr.dcfarris@gmail.com>
Co-authored-by: Ashcon Partovi <ashcon@partovi.net>
Co-authored-by: Dylan Conway <35280289+dylan-conway@users.noreply.github.com>
Co-authored-by: pfg <pfg@pfg.pw>
Co-authored-by: Colin McDonnell <colinmcd94@gmail.com>
Co-authored-by: dave caruso <me@paperdave.net>
Co-authored-by: zhiyuan <32867472+zhiyuang@users.noreply.github.com>
Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>
Co-authored-by: Kamil Ogórek <kamil.ogorek@gmail.com>
Co-authored-by: Ciro Spaciari <ciro.spaciari@gmail.com>
* __decorateClass, __decorateParam, lit test, wiptest test
* decorator factories test
* parameter decorator test
* test for decorators with constructor parameter properties
* Fix issue with `CryptoKey` and `SubtleCrypto` constructors
* Limit concurrency for GitHub Actions due to issues with cache poisoning
If multiple actions are running, sometimes the cache is poisoned from another action. We need to fix this, but this is an interim measure to make actions less flaky
* Make these tests better
* Move this to dependencies so the .a files upload
* Fixup
* temporary fix
* Limit concurrency for MacOS Object actions
* try againn
* againn
* Make `"tls"` an explicit object we pass instead of implicit top-level options
cc @Electroid @colinhacks
* Update server.zig
* Prefer `BUN_PORT` over `PORT`
* Fix typo in homebrew action
* Run homebrew action when release is edited
* Check published_at instead of draft in GitHub action
* Implement `process.release`
* Add missing dependencies to `make devcontainer`
* Allow overriding node polyfills via `BUN_OVERRIDE_MODULE_PATH`
* Add a stub for io_darwin on linux
cc @sno2 hopefully this helps but i'm not sure
* Add missing `break`
* Download more RAM
* feat(core): optimize zig slice (#1408)
* feat(core): optimize zig slice
* address concerns
* Remove webcrypto from vendor-without-check
* Update default tsconfig (#1418)
Co-authored-by: Colin McDonnell <colinmcd@alum.mit.edu>
* Enable `BUN_OVERRIDE_MODULE_PATH` in `bun wiptest`
* Upgrade WebKit
* space
* Support getting cached values and pending activity in the bindings generator
* Remove ✂️ function
* constructor creation, initializers, handle static and computed fields with decorators
* Updating libuwebsockets C API (#1423)
* fix for repeated regex match calls and fix for '^' in character classes (#1419)
* tests and formatting
* fix for ^ in character class
* formatting
* test for repeated match and exec calls
* create oniguruma regex for each exec/test
* check errorCode from creating oniguruma regexp and always return {} on failure
* oops
* call onig_initialize once
* fix incorrect escaping, removed unnecessary oniguruma settings
* tests for "-" and "^" in character classes
* free regex object before returns
* force gc for some tests
* Update React fizz server (#1432)
* Update fizz server
* Use production build
Co-authored-by: Colin McDonnell <colinmcd@alum.mit.edu>
* more decorator tests
* optional setup function for loading elements, simulate clicks in lit test
* fix createWriteStream (#1433)
* fix createWriteStream
* remove comment
* Update build docs and commands for dev containers (#1438)
* Update build documentation for dev containers
* Add devcontainer-rebuild make target
* Add make devcontainer-sh target
* Fix missing .PHONY for vendor-without-check (#1437)
* Fix check for ninja on Debian/Ubuntu (#1436)
Even though the package is named ninja-build, the ninja binary is still
named ninja, so use `which ninja` to check for it
* Fix#1410
woops
* await on DOMContentLoaded for elements instead of setup function
* avoid lowering class if no decorators
Co-authored-by: Jarred Sumner <709451+Jarred-Sumner@users.noreply.github.com>
Co-authored-by: Ashcon Partovi <ashcon@partovi.net>
Co-authored-by: Carter Snook <cartersnook04@gmail.com>
Co-authored-by: Colin McDonnell <colinmcd94@gmail.com>
Co-authored-by: Colin McDonnell <colinmcd@alum.mit.edu>
Co-authored-by: Ciro Spaciari <ciro.spaciari@gmail.com>
Co-authored-by: Lawrence Chen <54008264+lawrencecchen@users.noreply.github.com>
Co-authored-by: João Paquim <jpaquim@users.noreply.github.com>
This fixes a number of issues caused by not using live bindings when referencing bundled code. This also fixes an issue with libraries looping over `Object.keys(moduleNamespace)`
