v0.25.9

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• Better support building projects that use Yarn on Windows (#​3131, #​3663)

  With this release, you can now use esbuild to bundle projects that use Yarn Plug'n'Play on Windows on drives other than the C: drive. The problem was as follows:

  1. Yarn in Plug'n'Play mode on Windows stores its global module cache on the C: drive
  2. Some developers put their projects on the D: drive
  3. Yarn generates relative paths that use ../.. to get from the project directory to the cache directory
  4. Windows-style paths don't support directory traversal between drives via .. (so D:\.. is just D:)
  5. I didn't have access to a Windows machine for testing this edge case

  Yarn works around this edge case by pretending Windows-style paths beginning with C:\ are actually Unix-style paths beginning with /C:/, so the ../.. path segments are able to navigate across drives inside Yarn's implementation. This was broken for a long time in esbuild but I finally got access to a Windows machine and was able to debug and fix this edge case. So you should now be able to bundle these projects with esbuild.

• Preserve parentheses around function expressions (#​4252)

  The V8 JavaScript VM uses parentheses around function expressions as an optimization hint to immediately compile the function. Otherwise the function would be lazily-compiled, which has additional overhead if that function is always called immediately as lazy compilation involves parsing the function twice. You can read V8's blog post about this for more details.

  Previously esbuild did not represent parentheses around functions in the AST so they were lost during compilation. With this change, esbuild will now preserve parentheses around function expressions when they are present in the original source code. This means these optimization hints will not be lost when bundling with esbuild. In addition, esbuild will now automatically add this optimization hint to immediately-invoked function expressions. Here's an example:

  // Original code
  const fn0 = () => 0
  const fn1 = (() => 1)
  console.log(fn0, function() { return fn1() }())
  
  // Old output
  const fn0 = () => 0;
  const fn1 = () => 1;
  console.log(fn0, function() {
    return fn1();
  }());
  
  // New output
  const fn0 = () => 0;
  const fn1 = (() => 1);
  console.log(fn0, (function() {
    return fn1();
  })());

  Note that you do not want to wrap all function expressions in parentheses. This optimization hint should only be used for functions that are called on initial load. Using this hint for functions that are not called on initial load will unnecessarily delay the initial load. Again, see V8's blog post linked above for details.

• Update Go from 1.23.10 to 1.23.12 (#​4257, #​4258)

  This should have no effect on existing code as this version change does not change Go's operating system support. It may remove certain false positive reports (specifically CVE-2025-4674 and CVE-2025-47907) from vulnerability scanners that only detect which version of the Go compiler esbuild uses.

v0.25.8

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• Fix another TypeScript parsing edge case (#​4248)

  This fixes a regression with a change in the previous release that tries to more accurately parse TypeScript arrow functions inside the ?: operator. The regression specifically involves parsing an arrow function containing a #private identifier inside the middle of a ?: ternary operator inside a class body. This was fixed by propagating private identifier state into the parser clone used to speculatively parse the arrow function body. Here is an example of some affected code:

  class CachedDict {
    #has = (a: string) => dict.has(a);
    has = window
      ? (word: string): boolean => this.#has(word)
      : this.#has;
  }

• Fix a regression with the parsing of source phase imports

  The change in the previous release to parse source phase imports failed to properly handle the following cases:

  import source from 'bar'
  import source from from 'bar'
  import source type foo from 'bar'

  Parsing for these cases should now be fixed. The first case was incorrectly treated as a syntax error because esbuild was expecting the second case. And the last case was previously allowed but is now forbidden. TypeScript hasn't added this feature yet so it remains to be seen whether the last case will be allowed, but it's safer to disallow it for now. At least Babel doesn't allow the last case when parsing TypeScript, and Babel was involved with the source phase import specification.

v0.25.7

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• Parse and print JavaScript imports with an explicit phase (#​4238)

  This release adds basic syntax support for the defer and source import phases in JavaScript:

  • defer

    This is a stage 3 proposal for an upcoming JavaScript feature that will provide one way to eagerly load but lazily initialize imported modules. The imported module is automatically initialized on first use. Support for this syntax will also be part of the upcoming release of TypeScript 5.9. The syntax looks like this:

    import defer * as foo from "<specifier>";
    const bar = await import.defer("<specifier>");

    Note that this feature deliberately cannot be used with the syntax import defer foo from "<specifier>" or import defer { foo } from "<specifier>".

  • source

    This is a stage 3 proposal for an upcoming JavaScript feature that will provide another way to eagerly load but lazily initialize imported modules. The imported module is returned in an uninitialized state. Support for this syntax may or may not be a part of TypeScript 5.9 (see this issue for details). The syntax looks like this:

    import source foo from "<specifier>";
    const bar = await import.source("<specifier>");

    Note that this feature deliberately cannot be used with the syntax import defer * as foo from "<specifier>" or import defer { foo } from "<specifier>".

  This change only adds support for this syntax. These imports cannot currently be bundled by esbuild. To use these new features with esbuild's bundler, the imported paths must be external to the bundle and the output format must be set to esm.

• Support optionally emitting absolute paths instead of relative paths (#​338, #​2082, #​3023)

  This release introduces the --abs-paths= feature which takes a comma-separated list of situations where esbuild should use absolute paths instead of relative paths. There are currently three supported situations: code (comments and string literals), log (log message text and location info), and metafile (the JSON build metadata).

  Using absolute paths instead of relative paths is not the default behavior because it means that the build results are no longer machine-independent (which means builds are no longer reproducible). Absolute paths can be useful when used with certain terminal emulators that allow you to click on absolute paths in the terminal text and/or when esbuild is being automatically invoked from several different directories within the same script.

• Fix a TypeScript parsing edge case (#​4241)

  This release fixes an edge case with parsing an arrow function in TypeScript with a return type that's in the middle of a ?: ternary operator. For example:

  x = a ? (b) : c => d;
  y = a ? (b) : c => d : e;

  The : token in the value assigned to x pairs with the ? token, so it's not the start of a return type annotation. However, the first : token in the value assigned to y is the start of a return type annotation because after parsing the arrow function body, it turns out there's another : token that can be used to pair with the ? token. This case is notable as it's the first TypeScript edge case that esbuild has needed a backtracking parser to parse. It has been addressed by a quick hack (cloning the whole parser) as it's a rare edge case and esbuild doesn't otherwise need a backtracking parser. Hopefully this is sufficient and doesn't cause any issues.

• Inline small constant strings when minifying

  Previously esbuild's minifier didn't inline string constants because strings can be arbitrarily long, and this isn't necessarily a size win if the string is used more than once. Starting with this release, esbuild will now inline string constants when the length of the string is three code units or less. For example:

  // Original code
  const foo = 'foo'
  console.log({ [foo]: true })
  
  // Old output (with --minify --bundle --format=esm)
  var o="foo";console.log({[o]:!0});
  
  // New output (with --minify --bundle --format=esm)
  console.log({foo:!0});

  Note that esbuild's constant inlining only happens in very restrictive scenarios to avoid issues with TDZ handling. This change doesn't change when esbuild's constant inlining happens. It only expands the scope of it to include certain string literals in addition to numeric and boolean literals.

v0.25.6

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• Fix a memory leak when cancel() is used on a build context (#​4231)

  Calling rebuild() followed by cancel() in rapid succession could previously leak memory. The bundler uses a producer/consumer model internally, and the resource leak was caused by the consumer being termianted while there were still remaining unreceived results from a producer. To avoid the leak, the consumer now waits for all producers to finish before terminating.

• Support empty :is() and :where() syntax in CSS (#​4232)

  Previously using these selectors with esbuild would generate a warning. That warning has been removed in this release for these cases.

• Improve tree-shaking of try statements in dead code (#​4224)

  With this release, esbuild will now remove certain try statements if esbuild considers them to be within dead code (i.e. code that is known to not ever be evaluated). For example:

  // Original code
  return 'foo'
  try { return 'bar' } catch {}
  
  // Old output (with --minify)
  return"foo";try{return"bar"}catch{}
  
  // New output (with --minify)
  return"foo";

• Consider negated bigints to have no side effects

  While esbuild currently considers 1, -1, and 1n to all have no side effects, it didn't previously consider -1n to have no side effects. This is because esbuild does constant folding with numbers but not bigints. However, it meant that unused negative bigint constants were not tree-shaken. With this release, esbuild will now consider these expressions to also be side-effect free:

  // Original code
  let a = 1, b = -1, c = 1n, d = -1n
  
  // Old output (with --bundle --minify)
  (()=>{var n=-1n;})();
  
  // New output (with --bundle --minify)
  (()=>{})();

• Support a configurable delay in watch mode before rebuilding (#​3476, #​4178)

  The watch() API now takes a delay option that lets you add a delay (in milliseconds) before rebuilding when a change is detected in watch mode. If you use a tool that regenerates multiple source files very slowly, this should make it more likely that esbuild's watch mode won't generate a broken intermediate build before the successful final build. This option is also available via the CLI using the --watch-delay= flag.

  This should also help avoid confusion about the watch() API's options argument. It was previously empty to allow for future API expansion, which caused some people to think that the documentation was missing. It's no longer empty now that the watch() API has an option.

• Allow mixed array for entryPoints API option (#​4223)

  The TypeScript type definitions now allow you to pass a mixed array of both string literals and object literals to the entryPoints API option, such as ['foo.js', { out: 'lib', in: 'bar.js' }]. This was always possible to do in JavaScript but the TypeScript type definitions were previously too restrictive.

• Update Go from 1.23.8 to 1.23.10 (#​4204, #​4207)

  This should have no effect on existing code as this version change does not change Go's operating system support. It may remove certain false positive reports (specifically CVE-2025-4673 and CVE-2025-22874) from vulnerability scanners that only detect which version of the Go compiler esbuild uses.

• Experimental support for esbuild on OpenHarmony (#​4212)

  With this release, esbuild now publishes the @esbuild/openharmony-arm64 npm package for OpenHarmony. It contains a WebAssembly binary instead of a native binary because Go doesn't currently support OpenHarmony. Node does support it, however, so in theory esbuild should now work on OpenHarmony through WebAssembly.

  This change was contributed by @​hqzing.

v0.25.5

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• Fix a regression with browser in package.json (#​4187)

  The fix to #​4144 in version 0.25.3 introduced a regression that caused browser overrides specified in package.json to fail to override relative path names that end in a trailing slash. That behavior change affected the [email protected] package. This regression has been fixed, and now has test coverage.

• Add support for certain keywords as TypeScript tuple labels (#​4192)

  Previously esbuild could incorrectly fail to parse certain keywords as TypeScript tuple labels that are parsed by the official TypeScript compiler if they were followed by a ? modifier. These labels included function, import, infer, new, readonly, and typeof. With this release, these keywords will now be parsed correctly. Here's an example of some affected code:

  type Foo = [
    value: any,
    readonly?: boolean, // This is now parsed correctly
  ]

• Add CSS prefixes for the stretch sizing value (#​4184)

  This release adds support for prefixing CSS declarations such as div { width: stretch }. That CSS is now transformed into this depending on what the --target= setting includes:

  div {
    width: -webkit-fill-available;
    width: -moz-available;
    width: stretch;
  }

v0.25.4

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• Add simple support for CORS to esbuild's development server (#​4125)

  Starting with version 0.25.0, esbuild's development server is no longer configured to serve cross-origin requests. This was a deliberate change to prevent any website you visit from accessing your running esbuild development server. However, this change prevented (by design) certain use cases such as "debugging in production" by having your production website load code from localhost where the esbuild development server is running.

  To enable this use case, esbuild is adding a feature to allow Cross-Origin Resource Sharing (a.k.a. CORS) for simple requests. Specifically, passing your origin to the new cors option will now set the Access-Control-Allow-Origin response header when the request has a matching Origin header. Note that this currently only works for requests that don't send a preflight OPTIONS request, as esbuild's development server doesn't currently support OPTIONS requests.

  Some examples:

  • CLI:

    esbuild --servedir=. --cors-origin=https://example.com
    

  • JS:

    const ctx = await esbuild.context({})
    await ctx.serve({
      servedir: '.',
      cors: {
        origin: 'https://example.com',
      },
    })

  • Go:

    ctx, _ := api.Context(api.BuildOptions{})
    ctx.Serve(api.ServeOptions{
      Servedir: ".",
      CORS: api.CORSOptions{
        Origin: []string{"https://example.com"},
      },
    })

  The special origin * can be used to allow any origin to access esbuild's development server. Note that this means any website you visit will be able to read everything served by esbuild.

• Pass through invalid URLs in source maps unmodified (#​4169)

  This fixes a regression in version 0.25.0 where sources in source maps that form invalid URLs were not being passed through to the output. Version 0.25.0 changed the interpretation of sources from file paths to URLs, which means that URL parsing can now fail. Previously URLs that couldn't be parsed were replaced with the empty string. With this release, invalid URLs in sources should now be passed through unmodified.

• Handle exports named __proto__ in ES modules (#​4162, #​4163)

  In JavaScript, the special property name __proto__ sets the prototype when used inside an object literal. Previously esbuild's ESM-to-CommonJS conversion didn't special-case the property name of exports named __proto__ so the exported getter accidentally became the prototype of the object literal. It's unclear what this affects, if anything, but it's better practice to avoid this by using a computed property name in this case.

  This fix was contributed by @​magic-akari.

v0.25.3

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• Fix lowered async arrow functions before super() (#​4141, #​4142)

  This change makes it possible to call an async arrow function in a constructor before calling super() when targeting environments without async support, as long as the function body doesn't reference this. Here's an example (notice the change from this to null):

  // Original code
  class Foo extends Object {
    constructor() {
      (async () => await foo())()
      super()
    }
  }
  
  // Old output (with --target=es2016)
  class Foo extends Object {
    constructor() {
      (() => __async(this, null, function* () {
        return yield foo();
      }))();
      super();
    }
  }
  
  // New output (with --target=es2016)
  class Foo extends Object {
    constructor() {
      (() => __async(null, null, function* () {
        return yield foo();
      }))();
      super();
    }
  }

  Some background: Arrow functions with the async keyword are transformed into generator functions for older language targets such as --target=es2016. Since arrow functions capture this, the generated code forwards this into the body of the generator function. However, JavaScript class syntax forbids using this in a constructor before calling super(), and this forwarding was problematic since previously happened even when the function body doesn't use this. Starting with this release, esbuild will now only forward this if it's used within the function body.

  This fix was contributed by @​magic-akari.

• Fix memory leak with --watch=true (#​4131, #​4132)

  This release fixes a memory leak with esbuild when --watch=true is used instead of --watch. Previously using --watch=true caused esbuild to continue to use more and more memory for every rebuild, but --watch=true should now behave like --watch and not leak memory.

  This bug happened because esbuild disables the garbage collector when it's not run as a long-lived process for extra speed, but esbuild's checks for which arguments cause esbuild to be a long-lived process weren't updated for the new --watch=true style of boolean command-line flags. This has been an issue since this boolean flag syntax was added in version 0.14.24 in 2022. These checks are unfortunately separate from the regular argument parser because of how esbuild's internals are organized (the command-line interface is exposed as a separate Go API so you can build your own custom esbuild CLI).

  This fix was contributed by @​mxschmitt.

• More concise output for repeated legal comments (#​4139)

  Some libraries have many files and also use the same legal comment text in all files. Previously esbuild would copy each legal comment to the output file. Starting with this release, legal comments duplicated across separate files will now be grouped in the output file by unique comment content.

• Allow a custom host with the development server (#​4110)

  With this release, you can now use a custom non-IP host with esbuild's local development server (either with --serve= for the CLI or with the serve() call for the API). This was previously possible, but was intentionally broken in version 0.25.0 to fix a security issue. This change adds the functionality back except that it's now opt-in and only for a single domain name that you provide.

  For example, if you add a mapping in your /etc/hosts file from local.example.com to 127.0.0.1 and then use esbuild --serve=local.example.com:8000, you will now be able to visit http://local.example.com:8000/ in your browser and successfully connect to esbuild's development server (doing that would previously have been blocked by the browser). This should also work with HTTPS if it's enabled (see esbuild's documentation for how to do that).

• Add a limit to CSS nesting expansion (#​4114)

  With this release, esbuild will now fail with an error if there is too much CSS nesting expansion. This can happen when nested CSS is converted to CSS without nesting for older browsers as expanding CSS nesting is inherently exponential due to the resulting combinatorial explosion. The expansion limit is currently hard-coded and cannot be changed, but is extremely unlikely to trigger for real code. It exists to prevent esbuild from using too much time and/or memory. Here's an example:

  a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{color:red}}}}}}}}}}}}}}}}}}}}

  Previously, transforming this file with --target=safari1 took 5 seconds and generated 40mb of CSS. Trying to do that will now generate the following error instead:

  ✘ [ERROR] CSS nesting is causing too much expansion
  
      example.css:1:60:
        1 │ a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{a,b{color:red}}}}}}}}}}}}}}}}}}}}
          ╵                                                             ^
  
    CSS nesting expansion was terminated because a rule was generated with 65536 selectors. This limit
    exists to prevent esbuild from using too much time and/or memory. Please change your CSS to use
    fewer levels of nesting.
  

• Fix path resolution edge case (#​4144)

  This fixes an edge case where esbuild's path resolution algorithm could deviate from node's path resolution algorithm. It involves a confusing situation where a directory shares the same file name as a file (but without the file extension). See the linked issue for specific details. This appears to be a case where esbuild is correctly following node's published resolution algorithm but where node itself is doing something different. Specifically the step LOAD_AS_FILE appears to be skipped when the input ends with ... This release changes esbuild's behavior for this edge case to match node's behavior.

• Update Go from 1.23.7 to 1.23.8 (#​4133, #​4134)

  This should have no effect on existing code as this version change does not change Go's operating system support. It may remove certain reports from vulnerability scanners that detect which version of the Go compiler esbuild uses, such as for CVE-2025-22871.

  As a reminder, esbuild's development server is intended for development, not for production, so I do not consider most networking-related vulnerabilities in Go to be vulnerabilities in esbuild. Please do not use esbuild's development server in production.