Fix a regression with whitespace inside :is() (#3265)

The change to parse the contents of :is() in version 0.18.14 introduced a regression that incorrectly flagged the contents as a syntax error if the contents started with a whitespace token (for example div:is( .foo ) {}). This regression has been fixed.

Add the --serve-fallback= option (#2904)

The web server built into esbuild serves the latest in-memory results of the configured build. If the requested path doesn't match any in-memory build result, esbuild also provides the --servedir= option to tell esbuild to serve the requested path from that directory instead. And if the requested path doesn't match either of those things, esbuild will either automatically generate a directory listing (for directories) or return a 404 error.

Starting with this release, that last step can now be replaced with telling esbuild to serve a specific HTML file using the --serve-fallback= option. This can be used to provide a "not found" page for missing URLs. It can also be used to implement a single-page app that mutates the current URL and therefore requires the single app entry point to be served when the page is loaded regardless of whatever the current URL is.

Use the tsconfig field in package.json during extends resolution (#3247)

This release adds a feature from TypeScript 3.2 where if a tsconfig.json file specifies a package name in the extends field and that package's package.json file has a tsconfig field, the contents of that field are used in the search for the base tsconfig.json file.

Implement CSS nesting without :is() when possible (#1945)

Previously esbuild would always produce a warning when transforming nested CSS for a browser that doesn't support the :is() pseudo-class. This was because the nesting transform needs to generate an :is() in some complex cases which means the transformed CSS would then not work in that browser. However, the CSS nesting transform can often be done without generating an :is(). So with this release, esbuild will no longer warn when targeting browsers that don't support :is() in the cases where an :is() isn't needed to represent the nested CSS.

In addition, esbuild's nested CSS transform has been updated to avoid generating an :is() in cases where an :is() is preferable but there's a longer alternative that is also equivalent. This update means esbuild can now generate a combinatorial explosion of CSS for complex CSS nesting syntax when targeting browsers that don't support :is(). This combinatorial explosion is necessary to accurately represent the original semantics. For example:

/* Original code */
.first,
.second,
.third {
  & > & {
    color: red;
  }
}

/* Old output (with --target=chrome80) */
:is(.first, .second, .third) > :is(.first, .second, .third) {
  color: red;
}

/* New output (with --target=chrome80) */
.first > .first,
.first > .second,
.first > .third,
.second > .first,
.second > .second,
.second > .third,
.third > .first,
.third > .second,
.third > .third {
  color: red;
}

This change means you can now use CSS nesting with esbuild when targeting an older browser that doesn't support :is(). You'll now only get a warning from esbuild if you use complex CSS nesting syntax that esbuild can't represent in that older browser without using :is(). There are two such cases:

/* Case 1 */
a b {
  .foo & {
    color: red;
  }
}

/* Case 2 */
a {
  > b& {
    color: red;
  }
}

These two cases still need to use :is(), both for different reasons, and cannot be used when targeting an older browser that doesn't support :is():

/* Case 1 */
.foo :is(a b) {
  color: red;
}

/* Case 2 */
a > a:is(b) {
  color: red;
}

Automatically lower inset in CSS for older browsers

With this release, esbuild will now automatically expand the inset property to the top, right, bottom, and left properties when esbuild's target is set to a browser that doesn't support inset:

/* Original code */
.app {
  position: absolute;
  inset: 10px 20px;
}

/* Old output (with --target=chrome80) */
.app {
  position: absolute;
  inset: 10px 20px;
}

/* New output (with --target=chrome80) */
.app {
  position: absolute;
  top: 10px;
  right: 20px;
  bottom: 10px;
  left: 20px;
}

Add support for the new @starting-style CSS rule (#3249)

This at rule allow authors to start CSS transitions on first style update. That is, you can now make the transition take effect when the display property changes from none to block.

/* Original code */
@starting-style {
  h1 {
    background-color: transparent;
  }
}

/* Output */
@starting-style{h1{background-color:transparent}}

This was contributed by @yisibl.

Implement local CSS names (#20)

This release introduces two new loaders called global-css and local-css and two new pseudo-class selectors :local() and :global(). This is a partial implementation of the popular CSS modules approach for avoiding unintentional name collisions in CSS. I'm not calling this feature "CSS modules" because although some people in the community call it that, other people in the community have started using "CSS modules" to refer to something completely different and now CSS modules is an overloaded term.

Here's how this new local CSS name feature works with esbuild:

• Identifiers that look like .className and #idName are global with the global-css loader and local with the local-css loader. Global identifiers are the same across all files (the way CSS normally works) but local identifiers are different between different files. If two separate CSS files use the same local identifier .button, esbuild will automatically rename one of them so that they don't collide. This is analogous to how esbuild automatically renames JS local variables with the same name in separate JS files to avoid name collisions.

• It only makes sense to use local CSS names with esbuild when you are also using esbuild's bundler to bundle JS files that import CSS files. When you do that, esbuild will generate one export for each local name in the CSS file. The JS code can import these names and use them when constructing HTML DOM. For example:

  // app.js
  import { outerShell } from './app.css'
  const div = document.createElement('div')
  div.className = outerShell
  document.body.appendChild(div)
  

  /* app.css */
  .outerShell {
    position: absolute;
    inset: 0;
  }
  

  When you bundle this with esbuild app.js --bundle --loader:.css=local-css --outdir=out you'll now get this (notice how the local CSS name outerShell has been renamed):

  // out/app.js
  (() => {
    // app.css
    var outerShell = "app_outerShell";
  
    // app.js
    var div = document.createElement("div");
    div.className = outerShell;
    document.body.appendChild(div);
  })();
  

  /* out/app.css */
  .app_outerShell {
    position: absolute;
    inset: 0;
  }
  

  This feature only makes sense to use when bundling is enabled both because your code needs to import the renamed local names so that it can use them, and because esbuild needs to be able to process all CSS files containing local names in a single bundling operation so that it can successfully rename conflicting local names to avoid collisions.

• If you are in a global CSS file (with the global-css loader) you can create a local name using :local(), and if you are in a local CSS file (with the local-css loader) you can create a global name with :global(). So the choice of the global-css loader vs. the local-css loader just sets the default behavior for identifiers, but you can override it on a case-by-case basis as necessary. For example:

  :local(.button) {
    color: red;
  }
  :global(.button) {
    color: blue;
  }
  

  Processing this CSS file with esbuild with either the global-css or local-css loader will result in something like this:

  .stdin_button {
    color: red;
  }
  .button {
    color: blue;
  }
  

• The names that esbuild generates for local CSS names are an implementation detail and are not intended to be hard-coded anywhere. The only way you should be referencing the local CSS names in your JS or HTML is with an import statement in JS that is bundled with esbuild, as demonstrated above. For example, when --minify is enabled esbuild will use a different name generation algorithm which generates names that are as short as possible (analogous to how esbuild minifies local identifiers in JS).

• You can easily use both global CSS files and local CSS files simultaneously if you give them different file extensions. For example, you could pass --loader:.css=global-css and --loader:.module.css=local-css to esbuild so that .css files still use global names by default but .module.css files use local names by default.

• Keep in mind that the css loader is different than the global-css loader. The :local and :global annotations are not enabled with the css loader and will be passed through unchanged. This allows you to have the option of using esbuild to process CSS containing while preserving these annotations. It also means that local CSS names are disabled by default for now (since the css loader is currently the default for CSS files). The :local and :global syntax may be enabled by default in a future release.

Note that esbuild's implementation does not currently have feature parity with other implementations of modular CSS in similar tools. This is only a preliminary release with a partial implementation that includes some basic behavior to get the process started. Additional behavior may be added in future releases. In particular, this release does not implement:

• The composes pragma
• Tree shaking for unused local CSS
• Local names for keyframe animations, grid lines, @container, @counter-style, etc.

Issue #20 (the issue for this feature) is esbuild's most-upvoted issue! While this release still leaves that issue open, it's an important first step in that direction.

Parse :is, :has, :not, and :where in CSS

With this release, esbuild will now parse the contents of these pseudo-class selectors as a selector list. This means you will now get syntax warnings within these selectors for invalid selector syntax. It also means that esbuild's CSS nesting transform behaves slightly differently than before because esbuild is now operating on an AST instead of a token stream. For example:

/* Original code */
div {
  :where(.foo&) {
    color: red;
  }
}

/* Old output (with --target=chrome90) */
:where(.foo:is(div)) {
  color: red;
}

/* New output (with --target=chrome90) */
:where(div.foo) {
  color: red;
}

Add the --drop-labels= option (#2398)

If you want to conditionally disable some development-only code and have it not be present in the final production bundle, right now the most straightforward way of doing this is to use the --define: flag along with a specially-named global variable. For example, consider the following code:

function main() {
  DEV && doAnExpensiveCheck()
}

You can build this for development and production like this:

• Development: esbuild --define:DEV=true
• Production: esbuild --define:DEV=false

One drawback of this approach is that the resulting code crashes if you don't provide a value for DEV with --define:. In practice this isn't that big of a problem, and there are also various ways to work around this.

However, another approach that avoids this drawback is to use JavaScript label statements instead. That's what the --drop-labels= flag implements. For example, consider the following code:

function main() {
  DEV: doAnExpensiveCheck()
}

With this release, you can now build this for development and production like this:

• Development: esbuild
• Production: esbuild --drop-labels=DEV

This means that code containing optional development-only checks can now be written such that it's safe to run without any additional configuration. The --drop-labels= flag takes comma-separated list of multiple label names to drop.

Avoid causing unhandledRejection during shutdown (#3219)

All pending esbuild JavaScript API calls are supposed to fail if esbuild's underlying child process is unexpectedly terminated. This can happen if SIGINT is sent to the parent node process with Ctrl+C, for example. Previously doing this could also cause an unhandled promise rejection when esbuild attempted to communicate this failure to its own child process that no longer exists. This release now swallows this communication failure, which should prevent this internal unhandled promise rejection. This change means that you can now use esbuild's JavaScript API with a custom SIGINT handler that extends the lifetime of the node process without esbuild's internals causing an early exit due to an unhandled promise rejection.

Update browser compatibility table scripts

The scripts that esbuild uses to compile its internal browser compatibility table have been overhauled. Briefly:

• Converted from JavaScript to TypeScript
• Fixed some bugs that resulted in small changes to the table
• Added caniuse-lite and @mdn/browser-compat-data as new data sources (replacing manually-copied information)

This change means it's now much easier to keep esbuild's internal compatibility tables up to date. You can review the table changes here if you need to debug something about this change:

• JS table changes
• CSS table changes

Fix a panic with const enum inside parentheses (#3205)

This release fixes an edge case where esbuild could potentially panic if a TypeScript const enum statement was used inside of a parenthesized expression and was followed by certain other scope-related statements. Here's a minimal example that triggers this edge case:

(() => {
  const enum E { a };
  () => E.a
})

Allow a newline in the middle of TypeScript export type statement (#3225)

Previously esbuild incorrectly rejected the following valid TypeScript code:

export type
{ T };

export type
* as foo from 'bar';

Code that uses a newline after export type is now allowed starting with this release.

Fix cross-module inlining of string enums (#3210)

A refactoring typo in version 0.18.9 accidentally introduced a regression with cross-module inlining of string enums when combined with computed property accesses. This regression has been fixed.

Rewrite .js to .ts inside packages with exports (#3201)

Packages with the exports field are supposed to disable node's path resolution behavior that allows you to import a file with a different extension than the one in the source code (for example, importing foo/bar to get foo/bar.js). And TypeScript has behavior where you can import a non-existent .js file and you will get the .ts file instead. Previously the presence of the exports field caused esbuild to disable all extension manipulation stuff which included both node's implicit file extension searching and TypeScript's file extension swapping. However, TypeScript appears to always apply file extension swapping even in this case. So with this release, esbuild will now rewrite .js to .ts even inside packages with exports.

Fix a redirect edge case in esbuild's development server (#3208)

The development server canonicalizes directory URLs by adding a trailing slash. For example, visiting /about redirects to /about/ if /about/index.html would be served. However, if the requested path begins with two slashes, then the redirect incorrectly turned into a protocol-relative URL. For example, visiting //about redirected to //about/ which the browser turns into http://about/. This release fixes the bug by canonicalizing the URL path when doing this redirect.

Fix a TypeScript code generation edge case (#3199)

This release fixes a regression in version 0.18.4 where using a TypeScript namespace that exports a class declaration combined with --keep-names and a --target of es2021 or earlier could cause esbuild to export the class from the namespace using an incorrect name (notice the assignment to X2._Y vs. X2.Y):

// Original code

// Old output (with --keep-names --target=es2021)
var X;
((X2) => {
  const _Y = class _Y {
  };
  __name(_Y, "Y");
  let Y = _Y;
  X2._Y = _Y;
})(X || (X = {}));

// New output (with --keep-names --target=es2021)
var X;
((X2) => {
  const _Y = class _Y {
  };
  __name(_Y, "Y");
  let Y = _Y;
  X2.Y = _Y;
})(X || (X = {}));

Fix a tree-shaking bug that removed side effects (#3195)

This fixes a regression in version 0.18.4 where combining --minify-syntax with --keep-names could cause expressions with side effects after a function declaration to be considered side-effect free for tree shaking purposes. The reason was because --keep-names generates an expression statement containing a call to a helper function after the function declaration with a special flag that makes the function call able to be tree shaken, and then --minify-syntax could potentially merge that expression statement with following expressions without clearing the flag. This release fixes the bug by clearing the flag when merging expression statements together.

Fix an incorrect warning about CSS nesting (#3197)

A warning is currently generated when transforming nested CSS to a browser that doesn't support :is() because transformed nested CSS may need to use that feature to represent nesting. This was previously always triggered when an at-rule was encountered in a declaration context. Typically the only case you would encounter this is when using CSS nesting within a selector rule. However, there is a case where that's not true: when using a margin at-rule such as @top-left within @page. This release avoids incorrectly generating a warning in this case by checking that the at-rule is within a selector rule before generating a warning.

Fix await using declarations inside async generator functions

I forgot about the new await using declarations when implementing lowering for async generator functions in the previous release. This change fixes the transformation of await using declarations when they are inside lowered async generator functions:

// Original code
async function* foo() {
  await using x = await y
}

// Old output (with --supported:async-generator=false)
function foo() {
  return __asyncGenerator(this, null, function* () {
    await using x = yield new __await(y);
  });
}

// New output (with --supported:async-generator=false)
function foo() {
  return __asyncGenerator(this, null, function* () {
    var _stack = [];
    try {
      const x = __using(_stack, yield new __await(y), true);
    } catch (_) {
      var _error = _, _hasError = true;
    } finally {
      var _promise = __callDispose(_stack, _error, _hasError);
      _promise && (yield new __await(_promise));
    }
  });
}

Insert some prefixed CSS properties when appropriate (#3122)

With this release, esbuild will now insert prefixed CSS properties in certain cases when the target setting includes browsers that require a certain prefix. This is currently done for the following properties:

• appearance: *; => -webkit-appearance: *; -moz-appearance: *;
• backdrop-filter: *; => -webkit-backdrop-filter: *;
• background-clip: text => -webkit-background-clip: text;
• box-decoration-break: *; => -webkit-box-decoration-break: *;
• clip-path: *; => -webkit-clip-path: *;
• font-kerning: *; => -webkit-font-kerning: *;
• hyphens: *; => -webkit-hyphens: *;
• initial-letter: *; => -webkit-initial-letter: *;
• mask-image: *; => -webkit-mask-image: *;
• mask-origin: *; => -webkit-mask-origin: *;
• mask-position: *; => -webkit-mask-position: *;
• mask-repeat: *; => -webkit-mask-repeat: *;
• mask-size: *; => -webkit-mask-size: *;
• position: sticky; => position: -webkit-sticky;
• print-color-adjust: *; => -webkit-print-color-adjust: *;
• tab-size: *; => -moz-tab-size: *; -o-tab-size: *;
• text-decoration-color: *; => -webkit-text-decoration-color: *; -moz-text-decoration-color: *;
• text-decoration-line: *; => -webkit-text-decoration-line: *; -moz-text-decoration-line: *;
• text-decoration-skip: *; => -webkit-text-decoration-skip: *;
• text-emphasis-color: *; => -webkit-text-emphasis-color: *;
• text-emphasis-position: *; => -webkit-text-emphasis-position: *;
• text-emphasis-style: *; => -webkit-text-emphasis-style: *;
• text-orientation: *; => -webkit-text-orientation: *;
• text-size-adjust: *; => -webkit-text-size-adjust: *; -ms-text-size-adjust: *;
• user-select: *; => -webkit-user-select: *; -moz-user-select: *; -ms-user-select: *;

Here is an example:

/* Original code */
div {
  mask-image: url(x.png);
}

/* Old output (with --target=chrome99) */
div {
  mask-image: url(x.png);
}

/* New output (with --target=chrome99) */
div {
  -webkit-mask-image: url(x.png);
  mask-image: url(x.png);
}

Browser compatibility data was sourced from the tables on https://caniuse.com. Support for more CSS properties can be added in the future as appropriate.

Fix an obscure identifier minification bug (#2809)

Function declarations in nested scopes behave differently depending on whether or not "use strict" is present. To avoid generating code that behaves differently depending on whether strict mode is enabled or not, esbuild transforms nested function declarations into variable declarations. However, there was a bug where the generated variable name was not being recorded as declared internally, which meant that it wasn't being renamed correctly by the minifier and could cause a name collision. This bug has been fixed:

// Original code
const n = ''
for (let i of [0,1]) {
  function f () {}
}

// Old output (with --minify-identifiers --format=esm)
const f = "";
for (let o of [0, 1]) {
  let n = function() {
  };
  var f = n;
}

// New output (with --minify-identifiers --format=esm)
const f = "";
for (let o of [0, 1]) {
  let n = function() {
  };
  var t = n;
}

Fix a bug in esbuild's compatibility table script (#3179)

Setting esbuild's target to a specific JavaScript engine tells esbuild to use the JavaScript syntax feature compatibility data from https://kangax.github.io/compat-table/es6/ for that engine to determine which syntax features to allow. However, esbuild's script that builds this internal compatibility table had a bug that incorrectly ignores tests for engines that still have outstanding implementation bugs which were never fixed. This change fixes this bug with the script.

The only case where this changed the information in esbuild's internal compatibility table is that the hermes target is marked as no longer supporting destructuring. This is because there is a failing destructuring-related test for Hermes on https://kangax.github.io/compat-table/es6/. If you want to use destructuring with Hermes anyway, you can pass --supported:destructuring=true to esbuild to override the hermes target and force esbuild to accept this syntax.

This fix was contributed by @ArrayZoneYour.

Implement transforming async generator functions (#2780)

With this release, esbuild will now transform async generator functions into normal generator functions when the configured target environment doesn't support them. These functions behave similar to normal generator functions except that they use the Symbol.asyncIterator interface instead of the Symbol.iterator interface and the iteration methods return promises. Here's an example (helper functions are omitted):

// Original code
async function* foo() {
  yield Promise.resolve(1)
  await new Promise(r => setTimeout(r, 100))
  yield *[Promise.resolve(2)]
}
async function bar() {
  for await (const x of foo()) {
    console.log(x)
  }
}
bar()

// New output (with --target=es6)
function foo() {
  return __asyncGenerator(this, null, function* () {
    yield Promise.resolve(1);
    yield new __await(new Promise((r) => setTimeout(r, 100)));
    yield* __yieldStar([Promise.resolve(2)]);
  });
}
function bar() {
  return __async(this, null, function* () {
    try {
      for (var iter = __forAwait(foo()), more, temp, error; more = !(temp = yield iter.next()).done; more = false) {
        const x = temp.value;
        console.log(x);
      }
    } catch (temp) {
      error = [temp];
    } finally {
      try {
        more && (temp = iter.return) && (yield temp.call(iter));
      } finally {
        if (error)
          throw error[0];
      }
    }
  });
}
bar();

This is an older feature that was added to JavaScript in ES2018 but I didn't implement the transformation then because it's a rarely-used feature. Note that esbuild already added support for transforming for await loops (the other part of the asynchronous iteration proposal) a year ago, so support for asynchronous iteration should now be complete.

I have never used this feature myself and code that uses this feature is hard to come by, so this transformation has not yet been tested on real-world code. If you do write code that uses this feature, please let me know if esbuild's async generator transformation doesn't work with your code.

Add support for using declarations in TypeScript 5.2+ (#3191)

TypeScript 5.2 (due to be released in August of 2023) will introduce using declarations, which will allow you to automatically dispose of the declared resources when leaving the current scope. You can read the TypeScript PR for this feature for more information. This release of esbuild adds support for transforming this syntax to target environments without support for using declarations (which is currently all targets other than esnext). Here's an example (helper functions are omitted):

// Original code
class Foo {
  [Symbol.dispose]() {
    console.log('cleanup')
  }
}
using foo = new Foo;
foo.bar();

// New output (with --target=es6)
var _stack = [];
try {
  var Foo = class {
    [Symbol.dispose]() {
      console.log("cleanup");
    }
  };
  var foo = __using(_stack, new Foo());
  foo.bar();
} catch (_) {
  var _error = _, _hasError = true;
} finally {
  __callDispose(_stack, _error, _hasError);
}

The injected helper functions ensure that the method named Symbol.dispose is called on new Foo when control exits the scope. Note that as with all new JavaScript APIs, you'll need to polyfill Symbol.dispose if it's not present before you use it. This is not something that esbuild does for you because esbuild only handles syntax, not APIs. Polyfilling it can be done with something like this:

Symbol.dispose ||= Symbol('Symbol.dispose')

This feature also introduces await using declarations which are like using declarations but they call await on the disposal method (not on the initializer). Here's an example (helper functions are omitted):

// Original code
class Foo {
  async [Symbol.asyncDispose]() {
    await new Promise(done => {
      setTimeout(done, 1000)
    })
    console.log('cleanup')
  }
}
await using foo = new Foo;
foo.bar();

// New output (with --target=es2022)
var _stack = [];
try {
  var Foo = class {
    async [Symbol.asyncDispose]() {
      await new Promise((done) => {
        setTimeout(done, 1e3);
      });
      console.log("cleanup");
    }
  };
  var foo = __using(_stack, new Foo(), true);
  foo.bar();
} catch (_) {
  var _error = _, _hasError = true;
} finally {
  var _promise = __callDispose(_stack, _error, _hasError);
  _promise && await _promise;
}

The injected helper functions ensure that the method named Symbol.asyncDispose is called on new Foo when control exits the scope, and that the returned promise is awaited. Similarly to Symbol.dispose, you'll also need to polyfill Symbol.asyncDispose before you use it.

Add a --line-limit= flag to limit line length (#3170)

Long lines are common in minified code. However, many tools and text editors can't handle long lines. This release introduces the --line-limit= flag to tell esbuild to wrap lines longer than the provided number of bytes. For example, --line-limit=80 tells esbuild to insert a newline soon after a given line reaches 80 bytes in length. This setting applies to both JavaScript and CSS, and works even when minification is disabled. Note that turning this setting on will make your files bigger, as the extra newlines take up additional space in the file (even after gzip compression).