Changelog

Unreleased

Transform object rest properties

This release transforms object rest property bindings such as let {...x} = y when the language target is set to --target=es2017 or earlier.

If you're using Babel to transform your source code to ES6 for older browsers, this probably means esbuild's JavaScript API could now be a suitable replacement for Babel in your case. The only remaining features that esbuild can't yet transform to ES6 are a few very rarely used features that don't matter for the vast majority of real-world code (for async loops and async generators).

0.5.9

Add the --strict:nullish-coalescing option

This affects the transform for the ?? nullish coalescing operator. In loose mode (the default), a ?? b is transformed to a != null ? a : b. This works fine in all cases except when a is the special object document.all. In strict mode, a ?? b is transformed to a !== null && a !== void 0 ? a : b which works correctly with document.all. Enable --strict:nullish-coalescing if you need to use document.all with the ?? operator.
Add the --strict:class-fields option

This affects the transform for instance and static class fields. In loose mode (the default), class field initialization is transformed to a normal assignment. This is what the TypeScript compiler does by default. However, it doesn't follow the JavaScript specification exactly (e.g. it may call setter methods). Either enable --strict:class-fields or add useDefineForClassFields to your tsconfig.json file if you need accurate class field initialization.

Note that you can also just use --strict to enable strictness for all transforms instead of using --strict:... for each transform.

0.5.8

Transform async functions (#137)

This release transforms async functions into generator functions for older browsers when the language target is set to --target=es2016 or below. The transform esbuild uses is similar to the one used by the TypeScript compiler.

0.5.7

Transform private fields and private methods (#47)

Private names are an access control mechanism for classes. They begin with a # and are not accessible outside of the class they are declared in. Support for parsing this syntax was added in esbuild version 0.4.9 but the syntax was passed through unmodified, meaning it didn't work in older browsers.

This release adds support for transforming private fields and private methods for older browsers that don't support this syntax. This transform uses WeakMap and WeakSet to preserve the privacy properties of this feature, similar to the corresponding transforms in the Babel and TypeScript compilers.

This code:
```
class Counter {
  #count = 1
  get value() { return this.#count }
  increment() { ++this.#count }
}
```
is transformed into this code when using --target=es2020:
```
var _count;
class Counter {
  constructor() { _count.set(this, 1); }
  get value() { return __privateGet(this, _count); }
  increment() { __privateSet(this, _count, +__privateGet(this, _count) + 1); }
}
_count = new WeakMap();
```
Note that most modern JavaScript engines (V8, JavaScriptCore, and SpiderMonkey but not ChakraCore) may not have good performance characteristics for large WeakMap and WeakSet objects. Creating many instances of classes with private fields or private methods with this syntax transform active may cause a lot of overhead for the garbage collector. This is because modern engines (other than ChakraCore) store weak values in an actual map object instead of as hidden properties on the keys themselves, and large map objects can cause performance issues with garbage collection. See this reference for more information.
Fix re-exports when bundling

This is similar to the fix for re-exports in version 0.5.6 except that it applies when bundling, instead of just when transforming. It needed to be fixed differently because of how cross-file linking works when bundling.

0.5.6

Fix re-export statements (#190)

The previous release caused a regression due to some behind-the-scenes work for the upcoming code splitting feature. The re-export alias in statements of the form export { foo as bar } from 'path' could sometimes incorrectly be renamed to something else, such as foo becoming foo2. This release fixes the bug.

0.5.5

Implement logical assignment operator transforms

There are three new logical assignment operators: ??=, &&=, and ||=. With this release, you can now use them in older browsers by setting --target to a language version other than esnext. See the V8 blog post for more information about how they work.
Fix re-exports of a CommonJS module in esm format

Previously re-exports of an individual identifier from a CommonJS module generated JavaScript that crashed at run-time when using the esm output format. This was because esbuild always tries to generate "live" exports for CommonJS modules that always return the current value of the export instead of "dead" bindings that only return the initial value of the export. The bug happened because the ES6 module format doesn't have a way to forward a live binding to a CommonJS module as an ES6 export. The fix is to generate "dead" exports instead, which is the only available option in this edge case.

These input files:
```
// entry_point.js
export {foo} from './cjs-format.js'
```
```
// cjs-format.js
Object.defineProperty(exports, 'foo', {
  enumerable: true,
  get: () => Math.random(),
})
```
Now become this output file:
```
// cjs-format.js
var require_cjs_format = __commonJS((exports) => {
  Object.defineProperty(exports, "foo", {
    enumerable: true,
    get: () => Math.random()
  });
});

// entry_point.js
const cjs_format = __toModule(require_cjs_format());
const export_foo = cjs_format.foo; // This is a "dead" re-export
export {
  export_foo as foo
};
```

0.5.4

Source maps use / on Windows (#188)

Before generated source maps used \ on Windows, which meant that tools consuming these source maps (e.g. Chrome) didn't recognize these characters as path separators. Now all platforms consistently use / as a path separator.
Prevent input files from being overwritten

There are now checks in place to avoid input files being accidentally overwritten. This could easily happen with --bundle --outdir=. when bundling JavaScript files since the output file name ends up being the same as the entry point name, and is written to the same directory.

0.5.3

Special-case require in browserify bundles (#80 and #90)

Browserify generates code containing the expression typeof require == "function" && require which then ends up in a lot of npm packages. This expression is problematic because bundling involves statically determining all source files and their dependencies. Using require dynamically like this defeats the static analysis. It's also problematic because esbuild replaces typeof require == "function" with true since require is a function at compile-time when bundling. Then true && require becomes require in the generated code, which crashes at run time.

Previously esbuild would generate an error for these expressions. Now esbuild replaces typeof require == "function" && require with false when targeting the browser and require when targeting node. This matches the intent of the browserify prelude snippet and allows esbuild to build libraries containing this code without errors or warnings.
Allow dynamic dependencies (#113)

Bundling require() or import() when the argument isn't a string literal is a dynamic dependency. The dependency path relies on dynamic run-time behavior and cannot be statically determined by esbuild at bundle time.

Dynamic dependencies used to be an error but are now just a warning. Builds containing them now succeed and the generated code contains the require() or import() expression. This is useful either when the dynamic dependency is intentional or when you know the dynamic dependency won't ever be triggered. Doing this still generates a warning to alert you that some code was excluded from the bundle and because these expressions may still crash at run time if the imported path isn't valid.

0.5.2

Fix a regression with --define and identifiers

The API refactor introduced a regression where using a --define flag to replace something with an identifier followed by another --define flag unintentionally caused the first --define to use the value from the second --define for replacement. This regression was caused by a loop that was added around a Go closure, which caused all closures in that loop to close over the same variable. The bug has been fixed.
Fix interpretation of legacy --> single-line HTML comments

The --> sequence starts a single-line comment similar to //. This is legacy behavior from annex B under the name SingleLineHTMLCloseComment. However, --> was incorrectly treated as the start of a comment even when it didn't come at the beginning of the line. Now --> only starts a comment if there are no tokens before it on that line.
Allow shadowing of CommonJS variables (#165)

It's now no longer an error to re-declare exports, module, or require in a module scope. The re-declared symbol will just silently shadow the CommonJS variable with that name. This allows to use a variable called exports in an ES6 module, for example.

0.5.1

Go documentation was moved to godoc (#177)

The Go documentation is now in the source files itself instead of in an external Markdown file. View it online at https://godoc.org/github.com/evanw/esbuild/pkg/api and https://godoc.org/github.com/evanw/esbuild/pkg/cli.

The browser API now works in a script tag

The initial release of the browser API required a bundler to use correctly since it was in CommonJS format. This release adds the ability to use the browser API directly in HTML.

Here's an example using https://unpkg.com/ for simplicity, although you should consider hosting the files yourself:

<script src="https://unpkg.com/esbuild-wasm@0.5.1/lib/browser.js"></script>
<script>
  (async () => {
    const service = await esbuild.startService({
      wasmURL: 'https://unpkg.com/esbuild-wasm@0.5.1/esbuild.wasm'
    })
    try {
      const ts = 'enum Foo { A, B, C }'
      const { js } = await service.transform(ts, { loader: 'ts' })
      console.log(js)
    } finally {
      service.stop()
    }
  })()
</script>

0.5.0

Overhaul public-facing API code

This is a rewrite of all externally facing API code. It fixes some bugs and inconsistencies, adds some new features, and makes it easier to support various use cases going forward.

At a high-level, esbuild's API supports two separate operations: "build" and "transform". Building means reading from the file system and writing back to the file system. Transforming takes an input string and generates an output string. You should use the build API if you want to take advantage of esbuild's bundling capability, and you should use the transform API if you want to integrate esbuild as a library inside another tool (e.g. a "minify" plugin). This rewrite ensures the APIs for these two operations are exposed consistently for all ways of interacting with esbuild (both through the CLI and as a library).

Here are some of the highlights:
- There is now a public Go API (#152)
  
  The main API can be found in the github.com/evanw/esbuild/pkg/api module. It exposes the exact same features as the JavaScript API. This means you can use esbuild as a JavaScript transformation and bundling library from Go code without having to run esbuild as a child process. There is also the github.com/evanw/esbuild/pkg/cli module which can be used to wrap the esbuild CLI itself.
- There are now synchronous JavaScript APIs (#136)
  
  Sometimes JavaScript source transformations must be synchronous. For example, using esbuild's API to shim require() for .ts files was previously not possible because esbuild only had an asynchronous transform API.
  
  This release adds the new transformSync() and buildSync() synchronous functions to mirror the existing transform() and build() asynchronous functions. Note that these synchronous calls incur the cost of starting up a new child process each time, so you should only use these instead of startService() if you have to (or if you don't care about optimal performance).
- There is now an experimental browser-based API (#172)
  
  The esbuild-wasm package now has a file called browser.js that exposes a createService() API which is similar to the esbuild API available in node. You can either import the esbuild-wasm package using a bundler that respects the browser field in package.json or import the esbuild-wasm/lib/browser.js file directly.
  
  This is what esbuild's browser API looks like:
```
interface BrowserOptions {
  wasmURL: string
  worker?: boolean
}

interface BrowserService {
  transform(input: string, options: TransformOptions): Promise<TransformResult>
  stop(): void
}

declare function createService(options: BrowserOptions): Promise<BrowserService>
```
  You must provide the URL to the esbuild-wasm/esbuild.wasm file in wasmURL. The optional worker parameter can be set to false to load the WebAssembly module in the same thread instead of creating a worker thread. Using a worker thread is recommended because it means transforming will not block the main thread.
  
  This API is experimental and may be changed in the future depending on the feedback it gets.
- Error messages now use sourcefile (#131)
  
  Errors from transform API calls now use sourcefile as the the original file name if present. Previously the file name in error messages was always /input.js.

0.4.14

Do not reorder "use strict" after support code (#173)

Even when not in bundling mode, esbuild sometimes adds automatically-generated support code at the start of the output file. For example, using the ** operator with --target=es2015 causes let __pow = Math.pow to be inserted at the start of the file. This interfered with "use strict" directives, which must come first. Now "use strict" directives are written out first before any automatically-generated support code.
Fix bug with export star pointing to a re-export (#176)

This fixes a tree shaking bug that involves an export * from ... statement pointing to a file with a export {name} from ... statement. Now name will no longer be incorrectly removed from the bundle.

0.4.13

Fix possible name collision with CommonJS the target (#174)

A bug meant that the export objects for individual modules with the same filename could in some cases end up reusing the same name in the output file, which then caused a syntax error. This only happened with the cjs target. The bug has been fixed.

0.4.12

Support export * from ... for CommonJS modules (#159)

Wildcard re-exports are now supported when the exports come from a CommonJS or external module. Since CommonJS modules are not statically analyzable, this means in these cases the re-exports are evaluated at run time instead of at bundle time. Modules that re-export symbols this way will also be considered CommonJS modules during bundling because their exports are now also not statically analyzable.
Add 3rd-party library test coverage

From the esbuild repo, you can now run make test-extra to build some 3rd-party libraries (Rollup, Sucrase, and Esprima) with esbuild and run their test suites. This ensures that these libraries will continue to work as esbuild releases new features.

0.4.11

Fix top-level name minification with runtime

When not bundling, esbuild only minifies top-level names if the file is an ES6 module (as determined by the presence of an ES6 import or export statement). This determination had a bug where a non-module file was considered a module if esbuild automatically generated an import to some internal support code called the "runtime". For example, using the ** operator with --target=es2015 generates an import for the __pow runtime function. Runtime imports are now ignored for module determination, so an automatically-generated runtime import no longer causes top-level names to be minified.
Fix class name generation for default exports

Some changes to name generation for TypeScript decorators caused the generated class name for export default class statements to sometimes not match the name used for other references to that class in the same file. This bug has been fixed.

0.4.10

Initial implementation of TypeScript decorators (#104)

This release contains an initial implementation of the non-standard TypeScript-specific decorator syntax. This syntax transformation is enabled by default in esbuild, so no extra configuration is needed. The TypeScript compiler will need "experimentalDecorators": true configured in tsconfig.json for type checking to work with TypeScript decorators.

Here's an example of a method decorator:
```
function logged(target, key, descriptor) {
  let method = descriptor.value
  descriptor.value = function(...args) {
    let result = method.apply(this, args)
    let joined = args.map(x => JSON.stringify(x)).join(', ')
    console.log(`${key}(${joined}) => ${JSON.stringify(result)}`)
    return result
  }
}

class Example {
  @logged
  method(text: string) {
    return text + '!'
  }
}

const x = new Example
x.method('text')
```
There are four kinds of TypeScript decorators: class, method, parameter, and field decorators. See the TypeScript decorator documentation for more information. Note that esbuild only implements TypeScript's experimentalDecorators setting. It does not implement the emitDecoratorMetadata setting because that requires type information.
Fix order of side effects for computed fields

When transforming computed class fields, esbuild had a bug where the side effects of the field property names were not evaluated in source code order. The order of side effects now matches the order in the source code.
Fix private fields in TypeScript

This fixes a bug with private instance fields in TypeScript where the private field declaration was incorrectly removed during the TypeScript class field transform, which inlines the initializers into the constructor. Now the initializers are still moved to the constructor but the private field declaration is preserved without the initializer.

Note that since static private fields are not currently supported by the official TypeScript compiler, they are also not supported by esbuild in TypeScript files. They are supported by esbuild in JavaScript files, however.

0.4.9

Initial support for private names (#47)

Private names are an access control mechanism for classes. They begin with a # and are not accessible outside of the class they are declared in. The private name syntax can now be parsed, printed, and minified correctly. Transforming this syntax for older browsers is not supported yet. This is what the syntax looks like:
```
class Counter {
  #count = 1
  get value() { return this.#count }
  increment() { this.#count++ }
}
```
You can read more about these features here:
Initial support for logical assignment operators

This adds support for the three new logical assignment operators ||=, &&=, and ??=, which can now be parsed and passed through to the output. Transforming this syntax for older browsers is not supported yet. You can read more about these operators here: https://github.com/tc39/proposal-logical-assignment.
Data loaders now set "no side effects"

Files loaded using the json, text, base64, dataurl, and file loaders are now removed from the bundle if the files that import them never use the imports. This is the same behavior as the "sideEffects": false setting in package.json.

0.4.8

Add the --metafile flag (#140)

Pass --metafile=meta.json to write metadata about the build to the file meta.json. This includes information such as which files are in the bundle, what other files a given file depends on, and how much of each file ended up in the bundle. This is similar to the stats option in Webpack.

The format looks like this:

interface Metadata {
  inputs: {
    [path: string]: {
      bytes: number
      imports: {
        path: string
      }[]
    }
  }
  outputs: {
    [path: string]: {
      bytes: number
      inputs: {
        [path: string]: {
          bytesInOutput: number
        }
      }
    }
  }
}

Shorten numeric literals (#122)

Certain numeric literals now use shorter representations in the generated JavaScript code. For example, 123400000 is now written out as 1234e5.

0.4.7

Fixed sideEffects and nested directories

This fixes a bug where package.json files with "sideEffects": false were not respected for files in nested directories. When this bug occurred, bundles could be bigger than necessary. The sideEffects hint is now respected if any parent directory contains the hint instead of just the immediate enclosing directory.
Fixed sideEffects and default exports with side effects

This fixes a bug with default exports with side effects inside a "sideEffects": false context that were imported and used. These exports were incorrectly discarded instead of being retained, which could cause the resulting bundle to crash.

0.4.6

Respect the sideEffects field when tree shaking (#50)

Tree shaking now respects "sideEffects": false in package.json, which means esbuild now generates smaller bundles with certain libraries such as lodash-es. This setting is a convention from Webpack. Any files in a package with this setting will not be included in the bundle if they are imported using an ES6 import and then never used.

0.4.5

Fix a crash with more than 8 entry points (#162)

This bug was due to the wrong index being used for an internal bit set. That caused a crash due to an out-of-bounds array read when esbuild is run with more than 8 entry points. I now have test coverage for large numbers of entry points, so this should not happen again.
Fix slash characters in file loader (#164)

This fixes a bug where the base64-encoded hash included in the file name could sometimes contain a / character. The fix is to use the base64 character set for URL-encoding, which replaces the / character with a _ character.

0.4.4

Fix optional chaining with TypeScript operators (#168)

The work on optional chaining in the previous release introduced a regression where the TypeScript infix operators ! and <> incorrectly stopped the propagation of optional chaining. That meant a?.b!() and a?.b<T>() incorrectly behaved like (a?.b)() instead of a?.b(). This now has test coverage.
Add support for the "paths" field in tsconfig.json (#60 and #144)

This provides a way of remapping module paths to local file paths. It's relatively powerful because it supports wildcard patterns and multiple fallback locations. See the documentation in the TypeScript handbook for more information about how this feature works. This was contributed by @viankakrisna.
Add the file loader (#14 and #135)

The file loader copies the input file to the output folder and exports the path of the file as a string to any modules that import the file. For example, --loader:.png=file enables this loader for all imported .png files. This was contributed by @viankakrisna.
Add the --resolve-extensions flag (#142)

This lets you override the implicit extensions that are tested when importing a file. It must be a comma-separated list of extensions. For example, setting --resolve-extensions=.jsx,.js means import "./foo" will check for ./foo then ./foo.jsx then ./foo.js in that order. The behavior corresponds to the similarly-named feature in Webpack. This was contributed by @viankakrisna.

0.4.3

Fix bug with optional chaining parentheses (#156)

One edge case with JavaScript optional chaining syntax is that parentheses stop the chain. So a?.b.c will be undefined if a is nullish but (a?.b).c will crash if a is nullish.

This was handled correctly when lowering is enabled (i.e. when the language target is es2019 or below) but was not handled correctly when lowering is disabled (i.e. when the language target is es2020 or above). The output for (a?.b).c was incorrectly a?.b.c instead of (a?.b).c, which would no longer crash if a is nullish. The fix is to preserve the parentheses in the output.
Support for the PowerPC 64-bit Little Endian architecture on Linux (#146)

This was contributed by @runlevel5.

0.4.2

Bind imports to re-exports (#149)

This fixes a bug where imports of re-exported symbols were not correctly merged in some cases. This resulted in the generated code referencing symbols that were not declared, resulting in a crash.

0.4.1

Add a log level setting (#117)

You can now silence esbuild except for errors with --log-level=error, or except for errors and warnings with --log-level=warning.
Now jsconfig.json is an alternative to tsconfig.json (#132)

The "baseUrl" setting in tsconfig.json, which lets you avoid ../../ relative import paths, is respected by esbuild. With this change, esbuild will also check for this setting in jsconfig.json if no tsconfig.json file is found. This is relevant to some projects that use the TypeScript compiler with JavaScript files instead of TypeScript files. You can read more about this feature here. This was contributed by @viankakrisna.
Chinese translation of documentation (#129)

Both the readme and the architecture documentation have been translated into Chinese, which is available here: http://docs.breword.com/evanw-esbuild. This was contributed by @92hackers.
Async generator functions require --target=es2018

This fixes a bug where async generator functions were incorrectly allowed with --target=es2017, which is incorrect because the asynchronous iteration spec is part of ES2018.

0.4.0

Add the esm output format (#48)

It is now possible to generate a bundle in ES6 module format using --format=esm. The generated code uses ES6 import and export statements. This is useful for bundling code to be used as a library, for using in a <script type="module> tag in the browser, or for using with node's --experimental-modules flag. Note that CommonJS entry points bundled with this format will become a single default export, which is the same way node works.
Preliminary tree shaking support (#50)

Bundling now performs tree shaking, which is also known as dead code elimination. Every top-level statement is considered to be a separate part of the file, and unused parts without any side effects are not included in the bundle. This only really affects code using ES6 modules, so make sure you use ES6 modules to take advantage of tree shaking.

This is the initial release of tree shaking which lands the fundamental mechanism behind it. This release does not include the various annotations used by the community to indicate side-effect free code (e.g. "sideEffects": false and /*#__PURE__*/), so esbuild will likely generate somewhat bigger bundles than other bundlers. Support for these annotations will come in future releases.
Benchmarks have been re-run

This updates all of the bundlers used in the benchmark to their latest versions. Due to recent performance work, esbuild is now at least 100x faster than all other bundlers. I have also included a single-threaded version of esbuild for comparison since some people were wondering how much of esbuild's performance was due to multithreading.
Warnings about future syntax are now errors

This happens when an input file contains newer JavaScript syntax and --target is set to an earlier version of JavaScript than the syntax can be transformed to. These most of transforms will be implemented eventually, but for now some are still unimplemented. This was changed from a warning to an error because ignoring these warnings could result in broken code in older browsers, so these messages are more serious than warnings.
Using bundle-related flags without --bundle is now an error

This leaves the possibility open of using these flags for non-bundle mode in the future. For example, in the future --format may also work when not bundling.

0.3.9

Add the dataurl loader (#107)

This loader turns the file into a base64-encoded data URL. The mime type is automatically derived from the file extension, with the file contents used as a fallback. This was contributed by @viankakrisna.
Fix minification bug with external modules (#134)

When loading a module marked --external with require(), the resulting code was sometimes incorrectly minified when bundling. This now has test coverage.

0.3.8

Fix an issue that prevented non-inline source maps with the build() API (#130)

The issue happend when invoking esbuild.build({ sourcemap: true }) and was a regression due to the addition of inline source map support. This now has test coverage.

0.3.7

Add an unsupported build for ARM64 (#123)

Now you can npm install esbuild on a Linux ARM64 machine and it should work. This lets you run esbuild on a Raspberry Pi. Note that this target isn't officially supported because it's not covered by any automated tests. This was contributed by @violentmagician.

0.3.6

Fix a bug with JSX element contents that end in a multi-byte unicode character (#124)

Such characters are now preserved instead of being truncated.

0.3.5

Performance improvements

The parsing phase was failing to saturate all CPUs in many cases because input files were being read on a single goroutine in a blocking fashion. Each file is now read on its own goroutine and the parsing phase now saturates all CPUs.

With the performance improvements in this release and the previous release, the time to run the JavaScript benchmark has been reduced from 0.54s to 0.4s, which is approximately a 25% performance improvement.

0.3.4

Performance improvements

The GC is now disabled when running in build-and-exit mode, which is a noticeable speedup. This release also fixes some accidental O(n^2) behavior in the code that renames variables to avoid collisions in non-minify mode. This didn't affect any of esbuild's benchmarks but it did cause issues on certain other artificial test cases.

0.3.3

Support all unicode whitespace (#116)

The lexer now accepts all unicode characters in the WS category as valid whitespace to match the JavaScript standard.

0.3.2

Add some options related to source maps

There is now a sourcefile option to set the input file path for input files without a path. This happens in two cases: either using the service.transform() API or passing an input file using stdin.

This release also adds the inline value for the sourcemap option which inlines the source map as a base64-encoded data URL in the output file instead of writing the source map to a separate file.

0.3.1

Remove type-only exports from TypeScript (#110)

This fixes a bug where type-only exports in TypeScript files could in some cases generate an invalid export statement.

0.3.0

Support for stdin/stdout (#76)

You can now pass esbuild an input file over stdin instead of using a file path. Use the --loader=jsx syntax to set the loader instead of using the --loader:.js=jsx syntax.

Now if there is no output file, esbuild will write the output to stdout. Before this, esbuild would try to infer an output file based on the input file name. This is a breaking change so it was released with a minor version bump.

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