Releases · evanw/esbuild

22 Sep 02:07

v0.24.0

d34e79e

v0.24.0 Latest

Latest

This release deliberately contains backwards-incompatible changes. To avoid automatically picking up releases like this, you should either be pinning the exact version of esbuild in your package.json file (recommended) or be using a version range syntax that only accepts patch upgrades such as ^0.23.0 or ~0.23.0. See npm's documentation about semver for more information.

Drop support for older platforms (#3902)

This release drops support for the following operating system:
- macOS 10.15 Catalina
This is because the Go programming language dropped support for this operating system version in Go 1.23, and this release updates esbuild from Go 1.22 to Go 1.23. Go 1.23 now requires macOS 11 Big Sur or later.

Note that this only affects the binary esbuild executables that are published to the esbuild npm package. It's still possible to compile esbuild's source code for these older operating systems. If you need to, you can compile esbuild for yourself using an older version of the Go compiler (before Go version 1.23). That might look something like this:
```
git clone https://github.com/evanw/esbuild.git
cd esbuild
go build ./cmd/esbuild
./esbuild --version
```
Fix class field decorators in TypeScript if useDefineForClassFields is false (#3913)

Setting the useDefineForClassFields flag to false in tsconfig.json means class fields use the legacy TypeScript behavior instead of the standard JavaScript behavior. Specifically they use assign semantics instead of define semantics (e.g. setters are triggered) and fields without an initializer are not initialized at all. However, when this legacy behavior is combined with standard JavaScript decorators, TypeScript switches to always initializing all fields, even those without initializers. Previously esbuild incorrectly continued to omit field initializers for this edge case. These field initializers in this case should now be emitted starting with this release.
Avoid incorrect cycle warning with tsconfig.json multiple inheritance (#3898)

TypeScript 5.0 introduced multiple inheritance for tsconfig.json files where extends can be an array of file paths. Previously esbuild would incorrectly treat files encountered more than once when processing separate subtrees of the multiple inheritance hierarchy as an inheritance cycle. With this release, tsconfig.json files containing this edge case should work correctly without generating a warning.
Handle Yarn Plug'n'Play stack overflow with tsconfig.json (#3915)

Previously a tsconfig.json file that extends another file in a package with an exports map could cause a stack overflow when Yarn's Plug'n'Play resolution was active. This edge case should work now starting with this release.
Work around more issues with Deno 1.31+ (#3917)

This version of Deno broke the stdin and stdout properties on command objects for inherited streams, which matters when you run esbuild's Deno module as the entry point (i.e. when import.meta.main is true). Previously esbuild would crash in Deno 1.31+ if you ran esbuild like that. This should be fixed starting with this release.

This fix was contributed by @Joshix-1.

Assets 2

16 Aug 22:14

github-actions

v0.23.1

3327274

v0.23.1

Allow using the node: import prefix with es* targets (#3821)

The node: prefix on imports is an alternate way to import built-in node modules. For example, import fs from "fs" can also be written import fs from "node:fs". This only works with certain newer versions of node, so esbuild removes it when you target older versions of node such as with --target=node14 so that your code still works. With the way esbuild's platform-specific feature compatibility table works, this was added by saying that only newer versions of node support this feature. However, that means that a target such as --target=node18,es2022 removes the node: prefix because none of the es* targets are known to support this feature. This release adds the support for the node: flag to esbuild's internal compatibility table for es* to allow you to use compound targets like this:
```
// Original code
import fs from 'node:fs'
fs.open

// Old output (with --bundle --format=esm --platform=node --target=node18,es2022)
import fs from "fs";
fs.open;

// New output (with --bundle --format=esm --platform=node --target=node18,es2022)
import fs from "node:fs";
fs.open;
```
Fix a panic when using the CLI with invalid build flags if --analyze is present (#3834)

Previously esbuild's CLI could crash if it was invoked with flags that aren't valid for a "build" API call and the --analyze flag is present. This was caused by esbuild's internals attempting to add a Go plugin (which is how --analyze is implemented) to a null build object. The panic has been fixed in this release.
Fix incorrect location of certain error messages (#3845)

This release fixes a regression that caused certain errors relating to variable declarations to be reported at an incorrect location. The regression was introduced in version 0.18.7 of esbuild.
Print comments before case clauses in switch statements (#3838)

With this release, esbuild will attempt to print comments that come before case clauses in switch statements. This is similar to what esbuild already does for comments inside of certain types of expressions. Note that these types of comments are not printed if minification is enabled (specifically whitespace minification).
Fix a memory leak with pluginData (#3825)

With this release, the build context's internal pluginData cache will now be cleared when starting a new build. This should fix a leak of memory from plugins that return pluginData objects from onResolve and/or onLoad callbacks.

Assets 2

02 Jul 03:34

github-actions

v0.23.0

9d50680

v0.23.0

This release deliberately contains backwards-incompatible changes. To avoid automatically picking up releases like this, you should either be pinning the exact version of esbuild in your package.json file (recommended) or be using a version range syntax that only accepts patch upgrades such as ^0.22.0 or ~0.22.0. See npm's documentation about semver for more information.

Revert the recent change to avoid bundling dependencies for node (#3819)

This release reverts the recent change in version 0.22.0 that made --packages=external the default behavior with --platform=node. The default is now back to --packages=bundle.

I've just been made aware that Amazon doesn't pin their dependencies in their "AWS CDK" product, which means that whenever esbuild publishes a new release, many people (potentially everyone?) using their SDK around the world instantly starts using it without Amazon checking that it works first. This change in version 0.22.0 happened to break their SDK. I'm amazed that things haven't broken before this point. This revert attempts to avoid these problems for Amazon's customers. Hopefully Amazon will pin their dependencies in the future.

In addition, this is probably a sign that esbuild is used widely enough that it now needs to switch to a more complicated release model. I may have esbuild use a beta channel model for further development.
Fix preserving collapsed JSX whitespace (#3818)

When transformed, certain whitespace inside JSX elements is ignored completely if it collapses to an empty string. However, the whitespace should only be ignored if the JSX is being transformed, not if it's being preserved. This release fixes a bug where esbuild was previously incorrectly ignoring collapsed whitespace with --jsx=preserve. Here is an example:
```
// Original code
<Foo>
  <Bar />
</Foo>

// Old output (with --jsx=preserve)
<Foo><Bar /></Foo>;

// New output (with --jsx=preserve)
<Foo>
  <Bar />
</Foo>;
```

Assets 2

30 Jun 20:38

github-actions

v0.22.0

80c6e6e

v0.22.0

This release deliberately contains backwards-incompatible changes. To avoid automatically picking up releases like this, you should either be pinning the exact version of esbuild in your package.json file (recommended) or be using a version range syntax that only accepts patch upgrades such as ^0.21.0 or ~0.21.0. See npm's documentation about semver for more information.

Omit packages from bundles by default when targeting node (#1874, #2830, #2846, #2915, #3145, #3294, #3323, #3582, #3809, #3815)

This breaking change is an experiment. People are commonly confused when using esbuild to bundle code for node (i.e. for --platform=node) because some packages may not be intended for bundlers, and may use node-specific features that don't work with a bundler. Even though esbuild's "getting started" instructions say to use --packages=external to work around this problem, many people don't read the documentation and don't do this, and are then confused when it doesn't work. So arguably this is a bad default behavior for esbuild to have if people keep tripping over this.

With this release, esbuild will now omit packages from the bundle by default when the platform is node (i.e. the previous behavior of --packages=external is now the default in this case). Note that your dependencies must now be present on the file system when your bundle is run. If you don't want this behavior, you can do --packages=bundle to allow packages to be included in the bundle (i.e. the previous default behavior). Note that --packages=bundle doesn't mean all packages are bundled, just that packages are allowed to be bundled. You can still exclude individual packages from the bundle using --external: even when --packages=bundle is present.

The --packages= setting considers all import paths that "look like" package imports in the original source code to be package imports. Specifically import paths that don't start with a path segment of / or . or .. are considered to be package imports. The only two exceptions to this rule are subpath imports (which start with a # character) and TypeScript path remappings via paths and/or baseUrl in tsconfig.json (which are applied first).
Drop support for older platforms (#3802)

This release drops support for the following operating systems:
- Windows 7
- Windows 8
- Windows Server 2008
- Windows Server 2012
This is because the Go programming language dropped support for these operating system versions in Go 1.21, and this release updates esbuild from Go 1.20 to Go 1.22.

Note that this only affects the binary esbuild executables that are published to the esbuild npm package. It's still possible to compile esbuild's source code for these older operating systems. If you need to, you can compile esbuild for yourself using an older version of the Go compiler (before Go version 1.21). That might look something like this:
```
git clone https://github.com/evanw/esbuild.git
cd esbuild
go build ./cmd/esbuild
./esbuild.exe --version
```
In addition, this release increases the minimum required node version for esbuild's JavaScript API from node 12 to node 18. Node 18 is the oldest version of node that is still being supported (see node's release schedule for more information). This increase is because of an incompatibility between the JavaScript that the Go compiler generates for the esbuild-wasm package and versions of node before node 17.4 (specifically the crypto.getRandomValues function).
Update await using behavior to match TypeScript

TypeScript 5.5 subtly changes the way await using behaves. This release updates esbuild to match these changes in TypeScript. You can read more about these changes in microsoft/TypeScript#58624.
Allow es2024 as a target environment

The ECMAScript 2024 specification was just approved, so it has been added to esbuild as a possible compilation target. You can read more about the features that it adds here: https://2ality.com/2024/06/ecmascript-2024.html. The only addition that's relevant for esbuild is the regular expression /v flag. With --target=es2024, regular expressions that use the /v flag will now be passed through untransformed instead of being transformed into a call to new RegExp.
Publish binaries for OpenBSD on 64-bit ARM (#3665, #3674)

With this release, you should now be able to install the esbuild npm package in OpenBSD on 64-bit ARM, such as on an Apple device with an M1 chip.

This was contributed by @ikmckenz.
Publish binaries for WASI (WebAssembly System Interface) preview 1 (#3300, #3779)

The upcoming WASI (WebAssembly System Interface) standard is going to be a way to run WebAssembly outside of a JavaScript host environment. In this scenario you only need a .wasm file without any supporting JavaScript code. Instead of JavaScript providing the APIs for the host environment, the WASI standard specifies a "system interface" that WebAssembly code can access directly (e.g. for file system access).

Development versions of the WASI specification are being released using preview numbers. The people behind WASI are currently working on preview 2 but the Go compiler has released support for preview 1, which from what I understand is now considered an unsupported legacy release. However, some people have requested that esbuild publish binary executables that support WASI preview 1 so they can experiment with them.

This release publishes esbuild precompiled for WASI preview 1 to the @esbuild/wasi-preview1 package on npm (specifically the file @esbuild/wasi-preview1/esbuild.wasm). This binary executable has not been tested and won't be officially supported, as it's for an old preview release of a specification that has since moved in another direction. If it works for you, great! If not, then you'll likely have to wait for the ecosystem to evolve before using esbuild with WASI. For example, it sounds like perhaps WASI preview 1 doesn't include support for opening network sockets so esbuild's local development server is unlikely to work with WASI preview 1.
Warn about onResolve plugins not setting a path (#3790)

Plugins that return values from onResolve without resolving the path (i.e. without setting either path or external: true) will now cause a warning. This is because esbuild only uses return values from onResolve if it successfully resolves the path, and it's not good for invalid input to be silently ignored.
Add a new Go API for running the CLI with plugins (#3539)

With esbuild's Go API, you can now call cli.RunWithPlugins(args, plugins) to pass an array of esbuild plugins to be used during the build process. This allows you to create a CLI that behaves similarly to esbuild's CLI but with additional Go plugins enabled.

This was contributed by @edewit.

Assets 2

09 Jun 21:17

github-actions

v0.21.5

fc37c2f

v0.21.5

Fix Symbol.metadata on classes without a class decorator (#3781)

This release fixes a bug with esbuild's support for the decorator metadata proposal. Previously esbuild only added the Symbol.metadata property to decorated classes if there was a decorator on the class element itself. However, the proposal says that the Symbol.metadata property should be present on all classes that have any decorators at all, not just those with a decorator on the class element itself.
Allow unknown import attributes to be used with the copy loader (#3792)

Import attributes (the with keyword on import statements) are allowed to alter how that path is loaded. For example, esbuild cannot assume that it knows how to load ./bagel.js as type bagel:
```
// This is an error with "--bundle" without also using "--external:./bagel.js"
import tasty from "./bagel.js" with { type: "bagel" }
```
Because of that, bundling this code with esbuild is an error unless the file ./bagel.js is external to the bundle (such as with --bundle --external:./bagel.js).

However, there is an additional case where it's ok for esbuild to allow this: if the file is loaded using the copy loader. That's because the copy loader behaves similarly to --external in that the file is left external to the bundle. The difference is that the copy loader copies the file into the output folder and rewrites the import path while --external doesn't. That means the following will now work with the copy loader (such as with --bundle --loader:.bagel=copy):
```
// This is no longer an error with "--bundle" and "--loader:.bagel=copy"
import tasty from "./tasty.bagel" with { type: "bagel" }
```
Support import attributes with glob-style imports (#3797)

This release adds support for import attributes (the with option) to glob-style imports (dynamic imports with certain string literal patterns as paths). These imports previously didn't support import attributes due to an oversight. So code like this will now work correctly:
```
async function loadLocale(locale: string): Locale {
  const data = await import(`./locales/${locale}.data`, { with: { type: 'json' } })
  return unpackLocale(locale, data)
}
```
Previously this didn't work even though esbuild normally supports forcing the JSON loader using an import attribute. Attempting to do this used to result in the following error:
```
✘ [ERROR] No loader is configured for ".data" files: locales/en-US.data

    example.ts:2:28:
      2 │   const data = await import(`./locales/${locale}.data`, { with: { type: 'json' } })
        ╵                             ~~~~~~~~~~~~~~~~~~~~~~~~~~
```
In addition, this change means plugins can now access the contents of with for glob-style imports.
Support ${configDir} in tsconfig.json files (#3782)

This adds support for a new feature from the upcoming TypeScript 5.5 release. The character sequence ${configDir} is now respected at the start of baseUrl and paths values, which are used by esbuild during bundling to correctly map import paths to file system paths. This feature lets base tsconfig.json files specified via extends refer to the directory of the top-level tsconfig.json file. Here is an example:
```
{
  "compilerOptions": {
    "paths": {
      "js/*": ["${configDir}/dist/js/*"]
    }
  }
}
```
You can read more in TypeScript's blog post about their upcoming 5.5 release. Note that this feature does not make use of template literals (you need to use "${configDir}/dist/js/*" not `${configDir}/dist/js/*`). The syntax for tsconfig.json is still just JSON with comments, and JSON syntax does not allow template literals. This feature only recognizes ${configDir} in strings for certain path-like properties, and only at the beginning of the string.
Fix internal error with --supported:object-accessors=false (#3794)

This release fixes a regression in 0.21.0 where some code that was added to esbuild's internal runtime library of helper functions for JavaScript decorators fails to parse when you configure esbuild with --supported:object-accessors=false. The reason is that esbuild introduced code that does { get [name]() {} } which uses both the object-extensions feature for the [name] and the object-accessors feature for the get, but esbuild was incorrectly only checking for object-extensions and not for object-accessors. Additional tests have been added to avoid this type of issue in the future. A workaround for this issue in earlier releases is to also add --supported:object-extensions=false.

Assets 2

25 May 02:11

github-actions

v0.21.4

67cbf87

v0.21.4

Update support for import assertions and import attributes in node (#3778)

Import assertions (the assert keyword) have been removed from node starting in v22.0.0. So esbuild will now strip them and generate a warning with --target=node22 or above:
```
▲ [WARNING] The "assert" keyword is not supported in the configured target environment ("node22") [assert-to-with]

    example.mjs:1:40:
      1 │ import json from "esbuild/package.json" assert { type: "json" }
        │                                         ~~~~~~
        ╵                                         with

  Did you mean to use "with" instead of "assert"?
```
Import attributes (the with keyword) have been backported to node 18 starting in v18.20.0. So esbuild will no longer strip them with --target=node18.N if N is 20 or greater.

Fix for await transform when a label is present

This release fixes a bug where the for await transform, which wraps the loop in a try statement, previously failed to also move the loop's label into the try statement. This bug only affects code that uses both of these features in combination. Here's an example of some affected code:

// Original code
async function test() {
  outer: for await (const x of [Promise.resolve([0, 1])]) {
    for (const y of x) if (y) break outer
    throw 'fail'
  }
}

// Old output (with --target=es6)
function test() {
  return __async(this, null, function* () {
    outer: try {
      for (var iter = __forAwait([Promise.resolve([0, 1])]), more, temp, error; more = !(temp = yield iter.next()).done; more = false) {
        const x = temp.value;
        for (const y of x) if (y) break outer;
        throw "fail";
      }
    } catch (temp) {
      error = [temp];
    } finally {
      try {
        more && (temp = iter.return) && (yield temp.call(iter));
      } finally {
        if (error)
          throw error[0];
      }
    }
  });
}

// New output (with --target=es6)
function test() {
  return __async(this, null, function* () {
    try {
      outer: for (var iter = __forAwait([Promise.resolve([0, 1])]), more, temp, error; more = !(temp = yield iter.next()).done; more = false) {
        const x = temp.value;
        for (const y of x) if (y) break outer;
        throw "fail";
      }
    } catch (temp) {
      error = [temp];
    } finally {
      try {
        more && (temp = iter.return) && (yield temp.call(iter));
      } finally {
        if (error)
          throw error[0];
      }
    }
  });
}

Do additional constant folding after cross-module enum inlining (#3416, #3425)

This release adds a few more cases where esbuild does constant folding after cross-module enum inlining.

// Original code: enum.ts
export enum Platform {
  WINDOWS = 'windows',
  MACOS = 'macos',
  LINUX = 'linux',
}

// Original code: main.ts
import { Platform } from './enum';
declare const PLATFORM: string;
export function logPlatform() {
  if (PLATFORM == Platform.WINDOWS) console.log('Windows');
  else if (PLATFORM == Platform.MACOS) console.log('macOS');
  else if (PLATFORM == Platform.LINUX) console.log('Linux');
  else console.log('Other');
}

// Old output (with --bundle '--define:PLATFORM="macos"' --minify --format=esm)
function n(){"windows"=="macos"?console.log("Windows"):"macos"=="macos"?console.log("macOS"):"linux"=="macos"?console.log("Linux"):console.log("Other")}export{n as logPlatform};

// New output (with --bundle '--define:PLATFORM="macos"' --minify --format=esm)
function n(){console.log("macOS")}export{n as logPlatform};

Pass import attributes to on-resolve plugins (#3384, #3639, #3646)

With this release, on-resolve plugins will now have access to the import attributes on the import via the with property of the arguments object. This mirrors the with property of the arguments object that's already passed to on-load plugins. In addition, you can now pass with to the resolve() API call which will then forward that value on to all relevant plugins. Here's an example of a plugin that can now be written:

const examplePlugin = {
  name: 'Example plugin',
  setup(build) {
    build.onResolve({ filter: /.*/ }, args => {
      if (args.with.type === 'external')
        return { external: true }
    })
  }
}

require('esbuild').build({
  stdin: {
    contents: `
      import foo from "./foo" with { type: "external" }
      foo()
    `,
  },
  bundle: true,
  format: 'esm',
  write: false,
  plugins: [examplePlugin],
}).then(result => {
  console.log(result.outputFiles[0].text)
})

Formatting support for the @position-try rule (#3773)

Chrome shipped this new CSS at-rule in version 125 as part of the CSS anchor positioning API. With this release, esbuild now knows to expect a declaration list inside of the @position-try body block and will format it appropriately.
Always allow internal string import and export aliases (#3343)

Import and export names can be string literals in ES2022+. Previously esbuild forbid any usage of these aliases when the target was below ES2022. Starting with this release, esbuild will only forbid such usage when the alias would otherwise end up in output as a string literal. String literal aliases that are only used internally in the bundle and are "compiled away" are no longer errors. This makes it possible to use string literal aliases with esbuild's inject feature even when the target is earlier than ES2022.

Assets 2

15 May 20:53

github-actions

v0.21.3

efa3dd2

v0.21.3

Implement the decorator metadata proposal (#3760)

This release implements the decorator metadata proposal, which is a sub-proposal of the decorators proposal. Microsoft shipped the decorators proposal in TypeScript 5.0 and the decorator metadata proposal in TypeScript 5.2, so it's important that esbuild also supports both of these features. Here's a quick example:
```
// Shim the "Symbol.metadata" symbol
Symbol.metadata ??= Symbol('Symbol.metadata')

const track = (_, context) => {
  (context.metadata.names ||= []).push(context.name)
}

class Foo {
  @track foo = 1
  @track bar = 2
}

// Prints ["foo", "bar"]
console.log(Foo[Symbol.metadata].names)
```
⚠️ WARNING ⚠️

This proposal has been marked as "stage 3" which means "recommended for implementation". However, it's still a work in progress and isn't a part of JavaScript yet, so keep in mind that any code that uses JavaScript decorator metadata may need to be updated as the feature continues to evolve. If/when that happens, I will update esbuild's implementation to match the specification. I will not be supporting old versions of the specification.
Fix bundled decorators in derived classes (#3768)

In certain cases, bundling code that uses decorators in a derived class with a class body that references its own class name could previously generate code that crashes at run-time due to an incorrect variable name. This problem has been fixed. Here is an example of code that was compiled incorrectly before this fix:
```
class Foo extends Object {
  @(x => x) foo() {
    return Foo
  }
}
console.log(new Foo().foo())
```
Fix tsconfig.json files inside symlinked directories (#3767)

This release fixes an issue with a scenario involving a tsconfig.json file that extends another file from within a symlinked directory that uses the paths feature. In that case, the implicit baseURL value should be based on the real path (i.e. after expanding all symbolic links) instead of the original path. This was already done for other files that esbuild resolves but was not yet done for tsconfig.json because it's special-cased (the regular path resolver can't be used because the information inside tsconfig.json is involved in path resolution). Note that this fix no longer applies if the --preserve-symlinks setting is enabled.

Assets 2

12 May 20:33

github-actions

v0.21.2

b24180e

v0.21.2

Correct this in field and accessor decorators (#3761)

This release changes the value of this in initializers for class field and accessor decorators from the module-level this value to the appropriate this value for the decorated element (either the class or the instance). It was previously incorrect due to lack of test coverage. Here's an example of a decorator that doesn't work without this change:
```
const dec = () => function() { this.bar = true }
class Foo { @dec static foo }
console.log(Foo.bar) // Should be "true"
```
Allow es2023 as a target environment (#3762)

TypeScript recently added es2023 as a compilation target, so esbuild now supports this too. There is no difference between a target of es2022 and es2023 as far as esbuild is concerned since the 2023 edition of JavaScript doesn't introduce any new syntax features.

Assets 2

07 May 16:57

github-actions

v0.21.1

e876394

v0.21.1

Fix a regression with --keep-names (#3756)

The previous release introduced a regression with the --keep-names setting and object literals with get/set accessor methods, in which case the generated code contained syntax errors. This release fixes the regression:
```
// Original code
x = { get y() {} }

// Output from version 0.21.0 (with --keep-names)
x = { get y: /* @__PURE__ */ __name(function() {
}, "y") };

// Output from this version (with --keep-names)
x = { get y() {
} };
```

Assets 2

07 May 02:53

github-actions

v0.21.0

c6da2c3

v0.21.0

This release doesn't contain any deliberately-breaking changes. However, it contains a very complex new feature and while all of esbuild's tests pass, I would not be surprised if an important edge case turns out to be broken. So I'm releasing this as a breaking change release to avoid causing any trouble. As usual, make sure to test your code when you upgrade.

Implement the JavaScript decorators proposal (#104)

With this release, esbuild now contains an implementation of the upcoming JavaScript decorators proposal. This is the same feature that shipped in TypeScript 5.0 and has been highly-requested on esbuild's issue tracker. You can read more about them in that blog post and in this other (now slightly outdated) extensive blog post here: https://2ality.com/2022/10/javascript-decorators.html. Here's a quick example:
```
const log = (fn, context) => function() {
  console.log(`before ${context.name}`)
  const it = fn.apply(this, arguments)
  console.log(`after ${context.name}`)
  return it
}

class Foo {
  @log static foo() {
    console.log('in foo')
  }
}

// Logs "before foo", "in foo", "after foo"
Foo.foo()
```
Note that this feature is different than the existing "TypeScript experimental decorators" feature that esbuild already implements. It uses similar syntax but behaves very differently, and the two are not compatible (although it's sometimes possible to write decorators that work with both). TypeScript experimental decorators will still be supported by esbuild going forward as they have been around for a long time, are very widely used, and let you do certain things that are not possible with JavaScript decorators (such as decorating function parameters). By default esbuild will parse and transform JavaScript decorators, but you can tell esbuild to parse and transform TypeScript experimental decorators instead by setting "experimentalDecorators": true in your tsconfig.json file.

Probably at least half of the work for this feature went into creating a test suite that exercises many of the proposal's edge cases: https://github.com/evanw/decorator-tests. It has given me a reasonable level of confidence that esbuild's initial implementation is acceptable. However, I don't have access to a significant sample of real code that uses JavaScript decorators. If you're currently using JavaScript decorators in a real code base, please try out esbuild's implementation and let me know if anything seems off.

⚠️ WARNING ⚠️

This proposal has been in the works for a very long time (work began around 10 years ago in 2014) and it is finally getting close to becoming part of the JavaScript language. However, it's still a work in progress and isn't a part of JavaScript yet, so keep in mind that any code that uses JavaScript decorators may need to be updated as the feature continues to evolve. The decorators proposal is pretty close to its final form but it can and likely will undergo some small behavioral adjustments before it ends up becoming a part of the standard. If/when that happens, I will update esbuild's implementation to match the specification. I will not be supporting old versions of the specification.

Optimize the generated code for private methods

Previously when lowering private methods for old browsers, esbuild would generate one WeakSet for each private method. This mirrors similar logic for generating one WeakSet for each private field. Using a separate WeakMap for private fields is necessary as their assignment can be observable:

let it
class Bar {
  constructor() {
    it = this
  }
}
class Foo extends Bar {
  #x = 1
  #y = null.foo
  static check() {
    console.log(#x in it, #y in it)
  }
}
try { new Foo } catch {}
Foo.check()

This prints true false because this partially-initialized instance has #x but not #y. In other words, it's not true that all class instances will always have all of their private fields. However, the assignment of private methods to a class instance is not observable. In other words, it's true that all class instances will always have all of their private methods. This means esbuild can lower private methods into code where all methods share a single WeakSet, which is smaller, faster, and uses less memory. Other JavaScript processing tools such as the TypeScript compiler already make this optimization. Here's what this change looks like:

// Original code
class Foo {
  #x() { return this.#x() }
  #y() { return this.#y() }
  #z() { return this.#z() }
}

// Old output (--supported:class-private-method=false)
var _x, x_fn, _y, y_fn, _z, z_fn;
class Foo {
  constructor() {
    __privateAdd(this, _x);
    __privateAdd(this, _y);
    __privateAdd(this, _z);
  }
}
_x = new WeakSet();
x_fn = function() {
  return __privateMethod(this, _x, x_fn).call(this);
};
_y = new WeakSet();
y_fn = function() {
  return __privateMethod(this, _y, y_fn).call(this);
};
_z = new WeakSet();
z_fn = function() {
  return __privateMethod(this, _z, z_fn).call(this);
};

// New output (--supported:class-private-method=false)
var _Foo_instances, x_fn, y_fn, z_fn;
class Foo {
  constructor() {
    __privateAdd(this, _Foo_instances);
  }
}
_Foo_instances = new WeakSet();
x_fn = function() {
  return __privateMethod(this, _Foo_instances, x_fn).call(this);
};
y_fn = function() {
  return __privateMethod(this, _Foo_instances, y_fn).call(this);
};
z_fn = function() {
  return __privateMethod(this, _Foo_instances, z_fn).call(this);
};

Fix an obscure bug with lowering class members with computed property keys

When class members that use newer syntax features are transformed for older target environments, they sometimes need to be relocated. However, care must be taken to not reorder any side effects caused by computed property keys. For example, the following code must evaluate a() then b() then c():
```
class Foo {
  [a()]() {}
  [b()];
  static { c() }
}
```
Previously esbuild did this by shifting the computed property key forward to the next spot in the evaluation order. Classes evaluate all computed keys first and then all static class elements, so if the last computed key needs to be shifted, esbuild previously inserted a static block at start of the class body, ensuring it came before all other static class elements:
```
var _a;
class Foo {
  constructor() {
    __publicField(this, _a);
  }
  static {
    _a = b();
  }
  [a()]() {
  }
  static {
    c();
  }
}
```
However, this could cause esbuild to accidentally generate a syntax error if the computed property key contains code that isn't allowed in a static block, such as an await expression. With this release, esbuild fixes this problem by shifting the computed property key backward to the previous spot in the evaluation order instead, which may push it into the extends clause or even before the class itself:
```
// Original code
class Foo {
  [a()]() {}
  [await b()];
  static { c() }
}

// Old output (with --supported:class-field=false)
var _a;
class Foo {
  constructor() {
    __publicField(this, _a);
  }
  static {
    _a = await b();
  }
  [a()]() {
  }
  static {
    c();
  }
}

// New output (with --supported:class-field=false)
var _a, _b;
class Foo {
  constructor() {
    __publicField(this, _a);
  }
  [(_b = a(), _a = await b(), _b)]() {
  }
  static {
    c();
  }
}
```
Fix some --keep-names edge cases

The NamedEvaluation syntax-directed operation in the JavaScript specification gives certain anonymous expressions a name property depending on where they are in the syntax tree. For example, the following initializers convey a name value:
```
var foo = function() {}
var bar = class {}
console.log(foo.name, bar.name)
```
When you enable esbuild's --keep-names setting, esbuild generates additional code to represent this NamedEvaluation operation so that the value of the name property persists even when the identifiers are renamed (e.g. due to minification).

However, I recently learned that esbuild's implementation of NamedEvaluation is missing a few cases. Specifically esbuild was missing property definitions, class initializers, logical-assignment operators. These cases should now all be handled:
```
var obj = { foo: function() {} }
class Foo0 { foo = function() {} }
class Foo1 { static foo = function() {} }
class Foo2 { accessor foo = function() {} }
class Foo3 { static accessor foo = function() {} }
foo ||= function() {}
foo &&= function() {}
foo ??= function() {}
```

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