Sourced from esbuild's releases.

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)
    }

... (truncated)

Sourced from esbuild's changelog.

0.21.0

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)

... (truncated)

• c6da2c3 publish 0.21.0 to npm
• 4bc834c initial implementation of the decorators proposal (#3754)
• 07cdbe0 some small adjustments to runtime library code
• 71b3d9f split off lowerPrivateMethod from lowerMethod
• 0861625 printer: preserve single-line status of block body
• f426153 runtime: make some helper functions more compact
• 316eee5 simplify class lowering code generation
• ad2d0f6 split off CHANGELOG-2023.md
• e1b136d a few minor code adjustments to class lowering
• 5e7d1fc only --keep-names for lowered #private methods
• Additional commits viewable in compare view

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