Changelog: 2025

This changelog documents all esbuild versions published in the year 2025 (versions 0.25.0 through 0.27.2).

0.27.2

• Allow import path specifiers starting with #/ (#4361)

  Previously the specification for package.json disallowed import path specifiers starting with #/, but this restriction has recently been relaxed and support for it is being added across the JavaScript ecosystem. One use case is using it for a wildcard pattern such as mapping #/* to ./src/* (previously you had to use another character such as #_* instead, which was more confusing). There is some more context in nodejs/node#49182.

  This change was contributed by @hybrist.

• Automatically add the -webkit-mask prefix (#4357, #4358)

  This release automatically adds the -webkit- vendor prefix for the mask CSS shorthand property:

  /* Original code */
  main {
    mask: url(x.png) center/5rem no-repeat
  }
  
  /* Old output (with --target=chrome110) */
  main {
    mask: url(x.png) center/5rem no-repeat;
  }
  
  /* New output (with --target=chrome110) */
  main {
    -webkit-mask: url(x.png) center/5rem no-repeat;
    mask: url(x.png) center/5rem no-repeat;
  }
  

  This change was contributed by @BPJEnnova.

• Additional minification of switch statements (#4176, #4359)

  This release contains additional minification patterns for reducing switch statements. Here is an example:

  // Original code
  switch (x) {
    case 0:
      foo()
      break
    case 1:
    default:
      bar()
  }
  
  // Old output (with --minify)
  switch(x){case 0:foo();break;case 1:default:bar()}
  
  // New output (with --minify)
  x===0?foo():bar();
  

• Forbid using declarations inside switch clauses (#4323)

  This is a rare change to remove something that was previously possible. The Explicit Resource Management proposal introduced using declarations. These were previously allowed inside case and default clauses in switch statements. This had well-defined semantics and was already widely implemented (by V8, SpiderMonkey, TypeScript, esbuild, and others). However, it was considered to be too confusing because of how scope works in switch statements, so it has been removed from the specification. This edge case will now be a syntax error. See tc39/proposal-explicit-resource-management#215 and rbuckton/ecma262#14 for details.

  Here is an example of code that is no longer allowed:

  switch (mode) {
    case 'read':
      using readLock = db.read()
      return readAll(readLock)
  
    case 'write':
      using writeLock = db.write()
      return writeAll(writeLock)
  }
  

  That code will now have to be modified to look like this instead (note the additional { and } block statements around each case body):

  switch (mode) {
    case 'read': {
      using readLock = db.read()
      return readAll(readLock)
    }
    case 'write': {
      using writeLock = db.write()
      return writeAll(writeLock)
    }
  }
  

  This is not being released in one of esbuild's breaking change releases since this feature hasn't been finalized yet, and esbuild always tracks the current state of the specification (so esbuild's previous behavior was arguably incorrect).

0.27.1

• Fix bundler bug with var nested inside if (#4348)

  This release fixes a bug with the bundler that happens when importing an ES module using require (which causes it to be wrapped) and there's a top-level var inside an if statement without being wrapped in a { ... } block (and a few other conditions). The bundling transform needed to hoist these var declarations outside of the lazy ES module wrapper for correctness. See the issue for details.

• Fix minifier bug with for inside try inside label (#4351)

  This fixes an old regression from version v0.21.4. Some code was introduced to move the label inside the try statement to address a problem with transforming labeled for await loops to avoid the await (the transformation involves converting the for await loop into a for loop and wrapping it in a try statement). However, it introduces problems for cross-compiled JVM code that uses all three of these features heavily. This release restricts this transform to only apply to for loops that esbuild itself generates internally as part of the for await transform. Here is an example of some affected code:

  // Original code
  d: {
    e: {
      try {
        while (1) { break d }
      } catch { break e; }
    }
  }
  
  // Old output (with --minify)
  a:try{e:for(;;)break a}catch{break e}
  
  // New output (with --minify)
  a:e:try{for(;;)break a}catch{break e}
  

• Inline IIFEs containing a single expression (#4354)

  Previously inlining of IIFEs (immediately-invoked function expressions) only worked if the body contained a single return statement. Now it should also work if the body contains a single expression statement instead:

  // Original code
  const foo = () => {
    const cb = () => {
      console.log(x())
    }
    return cb()
  }
  
  // Old output (with --minify)
  const foo=()=>(()=>{console.log(x())})();
  
  // New output (with --minify)
  const foo=()=>{console.log(x())};
  

• The minifier now strips empty finally clauses (#4353)

  This improvement means that finally clauses containing dead code can potentially cause the associated try statement to be removed from the output entirely in minified builds:

  // Original code
  function foo(callback) {
    if (DEBUG) stack.push(callback.name);
    try {
      callback();
    } finally {
      if (DEBUG) stack.pop();
    }
  }
  
  // Old output (with --minify --define:DEBUG=false)
  function foo(a){try{a()}finally{}}
  
  // New output (with --minify --define:DEBUG=false)
  function foo(a){a()}
  

• Allow tree-shaking of the Symbol constructor

  With this release, calling Symbol is now considered to be side-effect free when the argument is known to be a primitive value. This means esbuild can now tree-shake module-level symbol variables:

  // Original code
  const a = Symbol('foo')
  const b = Symbol(bar)
  
  // Old output (with --tree-shaking=true)
  const a = Symbol("foo");
  const b = Symbol(bar);
  
  // New output (with --tree-shaking=true)
  const b = Symbol(bar);
  

0.27.0

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 ^0.26.0 or ~0.26.0. See npm's documentation about semver for more information.

• Use Uint8Array.fromBase64 if available (#4286)

  With this release, esbuild's binary loader will now use the new Uint8Array.fromBase64 function unless it's unavailable in the configured target environment. If it's unavailable, esbuild's previous code for this will be used as a fallback. Note that this means you may now need to specify target when using this feature with Node (for example --target=node22) unless you're using Node v25+.

• Update the Go compiler from v1.23.12 to v1.25.4 (#4208, #4311)

  This raises the operating system requirements for running esbuild:

  • Linux: now requires a kernel version of 3.2 or later
  • macOS: now requires macOS 12 (Monterey) or later

0.26.0

• Enable trusted publishing (#4281)

  GitHub and npm are recommending that maintainers for packages such as esbuild switch to trusted publishing. With this release, a VM on GitHub will now build and publish all of esbuild's packages to npm instead of me. In theory.

  Unfortunately there isn't really a way to test that this works other than to do it live. So this release is that live test. Hopefully this release is uneventful and is exactly the same as the previous one (well, except for the green provenance attestation checkmark on npm that happens with trusted publishing).

0.25.12

• Fix a minification regression with CSS media queries (#4315)

  The previous release introduced support for parsing media queries which unintentionally introduced a regression with the removal of duplicate media rules during minification. Specifically the grammar for @media <media-type> and <media-condition-without-or> { ... } was missing an equality check for the <media-condition-without-or> part, so rules with different suffix clauses in this position would incorrectly compare equal and be deduplicated. This release fixes the regression.

• Update the list of known JavaScript globals (#4310)

  This release updates esbuild's internal list of known JavaScript globals. These are globals that are known to not have side-effects when the property is accessed. For example, accessing the global Array property is considered to be side-effect free but accessing the global scrollY property can trigger a layout, which is a side-effect. This is used by esbuild's tree-shaking to safely remove unused code that is known to be side-effect free. This update adds the following global properties:

  From ES2017:

  • Atomics
  • SharedArrayBuffer

  From ES2020:

  • BigInt64Array
  • BigUint64Array

  From ES2021:

  • FinalizationRegistry
  • WeakRef

  From ES2025:

  • Float16Array
  • Iterator

  Note that this does not indicate that constructing any of these objects is side-effect free, just that accessing the identifier is side-effect free. For example, this now allows esbuild to tree-shake classes that extend from Iterator:

  // This can now be tree-shaken by esbuild:
  class ExampleIterator extends Iterator {}
  

• Add support for the new @view-transition CSS rule (#4313)

  With this release, esbuild now has improved support for pretty-printing and minifying the new @view-transition rule (which esbuild was previously unaware of):

  /* Original code */
  @view-transition {
    navigation: auto;
    types: check;
  }
  
  /* Old output */
  @view-transition { navigation: auto; types: check; }
  
  /* New output */
  @view-transition {
    navigation: auto;
    types: check;
  }
  

  The new view transition feature provides a mechanism for creating animated transitions between documents in a multi-page app. You can read more about view transition rules here.

  This change was contributed by @yisibl.

• Trim CSS rules that will never match

  The CSS minifier will now remove rules whose selectors contain :is() and :where() as those selectors will never match. These selectors can currently be automatically generated by esbuild when you give esbuild nonsensical input such as the following:

  /* Original code */
  div:before {
    color: green;
    &.foo {
      color: red;
    }
  }
  
  /* Old output (with --supported:nesting=false --minify) */
  div:before{color:green}:is().foo{color:red}
  
  /* New output (with --supported:nesting=false --minify) */
  div:before{color:green}
  

  This input is nonsensical because CSS nesting is (unfortunately) not supported inside of pseudo-elements such as :before. Currently esbuild generates a rule containing :is() in this case when you tell esbuild to transform nested CSS into non-nested CSS. I think it's reasonable to do that as it sort of helps explain what's going on (or at least indicates that something is wrong in the output). It shouldn't be present in minified code, however, so this release now strips it out.

0.25.11

• Add support for with { type: 'bytes' } imports (#4292)

  The import bytes proposal has reached stage 2.7 in the TC39 process, which means that although it isn't quite recommended for implementation, it's generally approved and ready for validation. Furthermore it has already been implemented by Deno and Webpack. So with this release, esbuild will also add support for this. It behaves exactly the same as esbuild's existing binary loader. Here's an example:

  import data from './image.png' with { type: 'bytes' }
  const view = new DataView(data.buffer, 0, 24)
  const width = view.getInt32(16)
  const height = view.getInt32(20)
  console.log('size:', width + '\xD7' + height)
  

• Lower CSS media query range syntax (#3748, #4293)

  With this release, esbuild will now transform CSS media query range syntax into equivalent syntax using min-/max- prefixes for older browsers. For example, the following CSS:

  @media (640px <= width <= 960px) {
    main {
      display: flex;
    }
  }
  

  will be transformed like this with a target such as --target=chrome100 (or more specifically with --supported:media-range=false if desired):

  @media (min-width: 640px) and (max-width: 960px) {
    main {
      display: flex;
    }
  }
  

0.25.10

• Fix a panic in a minification edge case (#4287)

  This release fixes a panic due to a null pointer that could happen when esbuild inlines a doubly-nested identity function and the final result is empty. It was fixed by emitting the value undefined in this case, which avoids the panic. This case must be rare since it hasn't come up until now. Here is an example of code that previously triggered the panic (which only happened when minifying):

  function identity(x) { return x }
  identity({ y: identity(123) })
  

• Fix @supports nested inside pseudo-element (#4265)

  When transforming nested CSS to non-nested CSS, esbuild is supposed to filter out pseudo-elements such as ::placeholder for correctness. The CSS nesting specification says the following:

  The nesting selector cannot represent pseudo-elements (identical to the behavior of the ':is()' pseudo-class). We’d like to relax this restriction, but need to do so simultaneously for both ':is()' and '&', since they’re intentionally built on the same underlying mechanisms.

  However, it seems like this behavior is different for nested at-rules such as @supports, which do work with pseudo-elements. So this release modifies esbuild's behavior to now take that into account:

  /* Original code */
  ::placeholder {
    color: red;
    body & { color: green }
    @supports (color: blue) { color: blue }
  }
  
  /* Old output (with --supported:nesting=false) */
  ::placeholder {
    color: red;
  }
  body :is() {
    color: green;
  }
  @supports (color: blue) {
     {
      color: blue;
    }
  }
  
  /* New output (with --supported:nesting=false) */
  ::placeholder {
    color: red;
  }
  body :is() {
    color: green;
  }
  @supports (color: blue) {
    ::placeholder {
      color: blue;
    }
  }
  

0.25.9

• 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.

0.25.8

• 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.

0.25.7

• 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.

0.25.6

• 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.

0.25.5

• 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 axios@0.30.0 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;
  }
  

0.25.4

• 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.

0.25.3

• 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.

0.25.2

• Support flags in regular expressions for the API (#4121)

  The JavaScript plugin API for esbuild takes JavaScript regular expression objects for the filter option. Internally these are translated into Go regular expressions. However, this translation previously ignored the flags property of the regular expression. With this release, esbuild will now translate JavaScript regular expression flags into Go regular expression flags. Specifically the JavaScript regular expression /\.[jt]sx?$/i is turned into the Go regular expression `(?i)\.[jt]sx?$` internally inside of esbuild's API. This should make it possible to use JavaScript regular expressions with the i flag. Note that JavaScript and Go don't support all of the same regular expression features, so this mapping is only approximate.

• Fix node-specific annotations for string literal export names (#4100)

  When node instantiates a CommonJS module, it scans the AST to look for names to expose via ESM named exports. This is a heuristic that looks for certain patterns such as exports.NAME = ... or module.exports = { ... }. This behavior is used by esbuild to "annotate" CommonJS code that was converted from ESM with the original ESM export names. For example, when converting the file export let foo, bar from ESM to CommonJS, esbuild appends this to the end of the file:

  // Annotate the CommonJS export names for ESM import in node:
  0 && (module.exports = {
    bar,
    foo
  });
  

  However, this feature previously didn't work correctly for export names that are not valid identifiers, which can be constructed using string literal export names. The generated code contained a syntax error. That problem is fixed in this release:

  // Original code
  let foo
  export { foo as "foo!" }
  
  // Old output (with --format=cjs --platform=node)
  ...
  0 && (module.exports = {
    "foo!"
  });
  
  // New output (with --format=cjs --platform=node)
  ...
  0 && (module.exports = {
    "foo!": null
  });
  

• Basic support for index source maps (#3439, #4109)

  The source map specification has an optional mode called index source maps that makes it easier for tools to create an aggregate JavaScript file by concatenating many smaller JavaScript files with source maps, and then generate an aggregate source map by simply providing the original source maps along with some offset information. My understanding is that this is rarely used in practice. I'm only aware of two uses of it in the wild: ClojureScript and Turbopack.

  This release provides basic support for indexed source maps. However, the implementation has not been tested on a real app (just on very simple test input). If you are using index source maps in a real app, please try this out and report back if anything isn't working for you.

  Note that this is also not a complete implementation. For example, index source maps technically allows nesting source maps to an arbitrary depth, while esbuild's implementation in this release only supports a single level of nesting. It's unclear whether supporting more than one level of nesting is important or not given the lack of available test cases.

  This feature was contributed by @clyfish.

0.25.1

• Fix incorrect paths in inline source maps (#4070, #4075, #4105)

  This fixes a regression from version 0.25.0 where esbuild didn't correctly resolve relative paths contained within source maps in inline sourceMappingURL data URLs. The paths were incorrectly being passed through as-is instead of being resolved relative to the source file containing the sourceMappingURL comment, which was due to the data URL not being a file URL. This regression has been fixed, and this case now has test coverage.

• Fix invalid generated source maps (#4080, #4082, #4104, #4107)

  This release fixes a regression from version 0.24.1 that could cause esbuild to generate invalid source maps. Specifically under certain conditions, esbuild could generate a mapping with an out-of-bounds source index. It was introduced by code that attempted to improve esbuild's handling of "null" entries in source maps (i.e. mappings with a generated position but no original position). This regression has been fixed.

  This fix was contributed by @jridgewell.

• Fix a regression with non-file source map paths (#4078)

  The format of paths in source maps that aren't in the file namespace was unintentionally changed in version 0.25.0. Path namespaces is an esbuild-specific concept that is optionally available for plugins to use to distinguish paths from file paths and from paths meant for other plugins. Previously the namespace was prepended to the path joined with a : character, but version 0.25.0 unintentionally failed to prepend the namespace. The previous behavior has been restored.

• Fix a crash with switch optimization (#4088)

  The new code in the previous release to optimize dead code in switch statements accidentally introduced a crash in the edge case where one or more switch case values include a function expression. This is because esbuild now visits the case values first to determine whether any cases are dead code, and then visits the case bodies once the dead code status is known. That triggered some internal asserts that guard against traversing the AST in an unexpected order. This crash has been fixed by changing esbuild to expect the new traversal ordering. Here's an example of affected code:

  switch (x) {
    case '':
      return y.map(z => z.value)
    case y.map(z => z.key).join(','):
      return []
  }
  

• Update Go from 1.23.5 to 1.23.7 (#4076, #4077)

  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.

  This PR was contributed by @MikeWillCook.

0.25.0

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 ^0.24.0 or ~0.24.0. See npm's documentation about semver for more information.

• Restrict access to esbuild's development server (GHSA-67mh-4wv8-2f99)

  This change addresses esbuild's first security vulnerability report. Previously esbuild set the Access-Control-Allow-Origin header to * to allow esbuild's development server to be flexible in how it's used for development. However, this allows the websites you visit to make HTTP requests to esbuild's local development server, which gives read-only access to your source code if the website were to fetch your source code's specific URL. You can read more information in the report.

  Starting with this release, CORS will now be disabled, and requests will now be denied if the host does not match the one provided to --serve=. The default host is 0.0.0.0, which refers to all of the IP addresses that represent the local machine (e.g. both 127.0.0.1 and 192.168.0.1). If you want to customize anything about esbuild's development server, you can put a proxy in front of esbuild and modify the incoming and/or outgoing requests.

  In addition, the serve() API call has been changed to return an array of hosts instead of a single host string. This makes it possible to determine all of the hosts that esbuild's development server will accept.

  Thanks to @sapphi-red for reporting this issue.

• Delete output files when a build fails in watch mode (#3643)

  It has been requested for esbuild to delete files when a build fails in watch mode. Previously esbuild left the old files in place, which could cause people to not immediately realize that the most recent build failed. With this release, esbuild will now delete all output files if a rebuild fails. Fixing the build error and triggering another rebuild will restore all output files again.

• Fix correctness issues with the CSS nesting transform (#3620, #3877, #3933, #3997, #4005, #4037, #4038)

  This release fixes the following problems:

  • Naive expansion of CSS nesting can result in an exponential blow-up of generated CSS if each nesting level has multiple selectors. Previously esbuild sometimes collapsed individual nesting levels using :is() to limit expansion. However, this collapsing wasn't correct in some cases, so it has been removed to fix correctness issues.

    /* Original code */
    .parent {
      > .a,
      > .b1 > .b2 {
        color: red;
      }
    }
    
    /* Old output (with --supported:nesting=false) */
    .parent > :is(.a, .b1 > .b2) {
      color: red;
    }
    
    /* New output (with --supported:nesting=false) */
    .parent > .a,
    .parent > .b1 > .b2 {
      color: red;
    }
    

    Thanks to @tim-we for working on a fix.

  • The & CSS nesting selector can be repeated multiple times to increase CSS specificity. Previously esbuild ignored this possibility and incorrectly considered && to have the same specificity as &. With this release, this should now work correctly:

    /* Original code (color should be red) */
    div {
      && { color: red }
      & { color: blue }
    }
    
    /* Old output (with --supported:nesting=false) */
    div {
      color: red;
    }
    div {
      color: blue;
    }
    
    /* New output (with --supported:nesting=false) */
    div:is(div) {
      color: red;
    }
    div {
      color: blue;
    }
    

    Thanks to @CPunisher for working on a fix.

  • Previously transforming nested CSS incorrectly removed leading combinators from within pseudoclass selectors such as :where(). This edge case has been fixed and how has test coverage.

    /* Original code */
    a b:has(> span) {
      a & {
        color: green;
      }
    }
    
    /* Old output (with --supported:nesting=false) */
    a :is(a b:has(span)) {
      color: green;
    }
    
    /* New output (with --supported:nesting=false) */
    a :is(a b:has(> span)) {
      color: green;
    }
    

    This fix was contributed by @NoremacNergfol.

  • The CSS minifier contains logic to remove the & selector when it can be implied, which happens when there is only one and it's the leading token. However, this logic was incorrectly also applied to selector lists inside of pseudo-class selectors such as :where(). With this release, the minifier will now avoid applying this logic in this edge case:

    /* Original code */
    .a {
      & .b { color: red }
      :where(& .b) { color: blue }
    }
    
    /* Old output (with --minify) */
    .a{.b{color:red}:where(.b){color:#00f}}
    
    /* New output (with --minify) */
    .a{.b{color:red}:where(& .b){color:#00f}}
    

• Fix some correctness issues with source maps (#1745, #3183, #3613, #3982)

  Previously esbuild incorrectly treated source map path references as file paths instead of as URLs. With this release, esbuild will now treat source map path references as URLs. This fixes the following problems with source maps:

  • File names in sourceMappingURL that contained a space previously did not encode the space as %20, which resulted in JavaScript tools (including esbuild) failing to read that path back in when consuming the generated output file. This should now be fixed.

  • Absolute URLs in sourceMappingURL that use the file:// scheme previously attempted to read from a folder called file:. These URLs should now be recognized and parsed correctly.

  • Entries in the sources array in the source map are now treated as URLs instead of file paths. The correct behavior for this is much more clear now that source maps has a formal specification. Many thanks to those who worked on the specification.

• Fix incorrect package for @esbuild/netbsd-arm64 (#4018)

  Due to a copy+paste typo, the binary published to @esbuild/netbsd-arm64 was not actually for arm64, and didn't run in that environment. This release should fix running esbuild in that environment (NetBSD on 64-bit ARM). Sorry about the mistake.

• Fix a minification bug with bitwise operators and bigints (#4065)

  This change removes an incorrect assumption in esbuild that all bitwise operators result in a numeric integer. That assumption was correct up until the introduction of bigints in ES2020, but is no longer correct because almost all bitwise operators now operate on both numbers and bigints. Here's an example of the incorrect minification:

  // Original code
  if ((a & b) !== 0) found = true
  
  // Old output (with --minify)
  a&b&&(found=!0);
  
  // New output (with --minify)
  (a&b)!==0&&(found=!0);
  

• Fix esbuild incorrectly rejecting valid TypeScript edge case (#4027)

  The following TypeScript code is valid:

  export function open(async?: boolean): void {
    console.log(async as boolean)
  }
  

  Before this version, esbuild would fail to parse this with a syntax error as it expected the token sequence async as ... to be the start of an async arrow function expression async as => .... This edge case should be parsed correctly by esbuild starting with this release.

• Transform BigInt values into constructor calls when unsupported (#4049)

  Previously esbuild would refuse to compile the BigInt literals (such as 123n) if they are unsupported in the configured target environment (such as with --target=es6). The rationale was that they cannot be polyfilled effectively because they change the behavior of JavaScript's arithmetic operators and JavaScript doesn't have operator overloading.

  However, this prevents using esbuild with certain libraries that would otherwise work if BigInt literals were ignored, such as with old versions of the buffer library before the library fixed support for running in environments without BigInt support. So with this release, esbuild will now turn BigInt literals into BigInt constructor calls (so 123n becomes BigInt(123)) and generate a warning in this case. You can turn off the warning with --log-override:bigint=silent or restore the warning to an error with --log-override:bigint=error if needed.

• Change how console API dropping works (#4020)

  Previously the --drop:console feature replaced all method calls off of the console global with undefined regardless of how long the property access chain was (so it applied to console.log() and console.log.call(console) and console.log.not.a.method()). However, it was pointed out that this breaks uses of console.log.bind(console). That's also incompatible with Terser's implementation of the feature, which is where this feature originally came from (it does support bind). So with this release, using this feature with esbuild will now only replace one level of method call (unless extended by call or apply) and will replace the method being called with an empty function in complex cases:

  // Original code
  const x = console.log('x')
  const y = console.log.call(console, 'y')
  const z = console.log.bind(console)('z')
  
  // Old output (with --drop-console)
  const x = void 0;
  const y = void 0;
  const z = (void 0)("z");
  
  // New output (with --drop-console)
  const x = void 0;
  const y = void 0;
  const z = (() => {
  }).bind(console)("z");
  

  This should more closely match Terser's existing behavior.

• Allow BigInt literals as define values

  With this release, you can now use BigInt literals as define values, such as with --define:FOO=123n. Previously trying to do this resulted in a syntax error.

• Fix a bug with resolve extensions in node_modules (#4053)

  The --resolve-extensions= option lets you specify the order in which to try resolving implicit file extensions. For complicated reasons, esbuild reorders TypeScript file extensions after JavaScript ones inside of node_modules so that JavaScript source code is always preferred to TypeScript source code inside of dependencies. However, this reordering had a bug that could accidentally change the relative order of TypeScript file extensions if one of them was a prefix of the other. That bug has been fixed in this release. You can see the issue for details.

• Better minification of statically-determined switch cases (#4028)

  With this release, esbuild will now try to trim unused code within switch statements when the test expression and case expressions are primitive literals. This can arise when the test expression is an identifier that is substituted for a primitive literal at compile time. For example:

  // Original code
  switch (MODE) {
    case 'dev':
      installDevToolsConsole()
      break
    case 'prod':
      return
    default:
      throw new Error
  }
  
  // Old output (with --minify '--define:MODE="prod"')
  switch("prod"){case"dev":installDevToolsConsole();break;case"prod":return;default:throw new Error}
  
  // New output (with --minify '--define:MODE="prod"')
  return;
  

• Emit /* @__KEY__ */ for string literals derived from property names (#4034)

  Property name mangling is an advanced feature that shortens certain property names for better minification (I say "advanced feature" because it's very easy to break your code with it). Sometimes you need to store a property name in a string, such as obj.get('foo') instead of obj.foo. JavaScript minifiers such as esbuild and Terser have a convention where a /* @__KEY__ */ comment before the string makes it behave like a property name. So obj.get(/* @__KEY__ */ 'foo') allows the contents of the string 'foo' to be shortened.

  However, esbuild sometimes itself generates string literals containing property names when transforming code, such as when lowering class fields to ES6 or when transforming TypeScript decorators. Previously esbuild didn't generate its own /* @__KEY__ */ comments in this case, which means that minifying your code by running esbuild again on its own output wouldn't work correctly (this does not affect people that both minify and transform their code in a single step).

  With this release, esbuild will now generate /* @__KEY__ */ comments for property names in generated string literals. To avoid lots of unnecessary output for people that don't use this advanced feature, the generated comments will only be present when the feature is active. If you want to generate the comments but not actually mangle any property names, you can use a flag that has no effect such as --reserve-props=., which tells esbuild to not mangle any property names (but still activates this feature).

• The text loader now strips the UTF-8 BOM if present (#3935)

  Some software (such as Notepad on Windows) can create text files that start with the three bytes 0xEF 0xBB 0xBF, which is referred to as the "byte order mark". This prefix is intended to be removed before using the text. Previously esbuild's text loader included this byte sequence in the string, which turns into a prefix of \uFEFF in a JavaScript string when decoded from UTF-8. With this release, esbuild's text loader will now remove these bytes when they occur at the start of the file.

• Omit legal comment output files when empty (#3670)

  Previously configuring esbuild with --legal-comment=external or --legal-comment=linked would always generate a .LEGAL.txt output file even if it was empty. Starting with this release, esbuild will now only do this if the file will be non-empty. This should result in a more organized output directory in some cases.

• Update Go from 1.23.1 to 1.23.5 (#4056, #4057)

  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.

  This PR was contributed by @MikeWillCook.

• Allow passing a port of 0 to the development server (#3692)

  Unix sockets interpret a port of 0 to mean "pick a random unused port in the ephemeral port range". However, esbuild's default behavior when the port is not specified is to pick the first unused port starting from 8000 and upward. This is more convenient because port 8000 is typically free, so you can for example restart the development server and reload your app in the browser without needing to change the port in the URL. Since esbuild is written in Go (which does not have optional fields like JavaScript), not specifying the port in Go means it defaults to 0, so previously passing a port of 0 to esbuild caused port 8000 to be picked.

  Starting with this release, passing a port of 0 to esbuild when using the CLI or the JS API will now pass port 0 to the OS, which will pick a random ephemeral port. To make this possible, the Port option in the Go API has been changed from uint16 to int (to allow for additional sentinel values) and passing a port of -1 in Go now picks a random port. Both the CLI and JS APIs now remap an explicitly-provided port of 0 into -1 for the internal Go API.

  Another option would have been to change Port in Go from uint16 to *uint16 (Go's closest equivalent of number | undefined). However, that would make the common case of providing an explicit port in Go very awkward as Go doesn't support taking the address of integer constants. This tradeoff isn't worth it as picking a random ephemeral port is a rare use case. So the CLI and JS APIs should now match standard Unix behavior when the port is 0, but you need to use -1 instead with Go API.

• Minification now avoids inlining constants with direct eval (#4055)

  Direct eval can be used to introduce a new variable like this:

  const variable = false
  ;(function () {
    eval("var variable = true")
    console.log(variable)
  })()
  

  Previously esbuild inlined variable here (which became false), which changed the behavior of the code. This inlining is now avoided, but please keep in mind that direct eval breaks many assumptions that JavaScript tools hold about normal code (especially when bundling) and I do not recommend using it. There are usually better alternatives that have a more localized impact on your code. You can read more about this here: https://esbuild.github.io/link/direct-eval/