v0.18.0

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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 ^0.17.0 or ~0.17.0. See npm's documentation about semver for more information.

The breaking changes in this release mainly focus on fixing some long-standing issues with esbuild's handling of tsconfig.json files. Here are all the changes in this release, in detail:

• Add a way to try esbuild online (#​797)

  There is now a way to try esbuild live on esbuild's website without installing it: https://esbuild.github.io/try/. In addition to being able to more easily evaluate esbuild, this should also make it more efficient to generate esbuild bug reports. For example, you can use it to compare the behavior of different versions of esbuild on the same input. The state of the page is stored in the URL for easy sharing. Many thanks to @​hyrious for creating https://hyrious.me/esbuild-repl/, which was the main inspiration for this addition to esbuild's website.

  Two forms of build options are supported: either CLI-style (example) or JS-style (example). Both are converted into a JS object that's passed to esbuild's WebAssembly API. The CLI-style argument parser is a custom one that simulates shell quoting rules, and the JS-style argument parser is also custom and parses a superset of JSON (basically JSON5 + regular expressions). So argument parsing is an approximate simulation of what happens for real but hopefully it should be close enough.

• Changes to esbuild's tsconfig.json support (#​3019):

  This release makes the following changes to esbuild's tsconfig.json support:

  • Using experimental decorators now requires "experimentalDecorators": true (#​104)

    Previously esbuild would always compile decorators in TypeScript code using TypeScript's experimental decorator transform. Now that standard JavaScript decorators are close to being finalized, esbuild will now require you to use "experimentalDecorators": true to do this. This new requirement makes it possible for esbuild to introduce a transform for standard JavaScript decorators in TypeScript code in the future. Such a transform has not been implemented yet, however.

  • TypeScript's target no longer affects esbuild's target (#​2628)

    Some people requested that esbuild support TypeScript's target setting, so support for it was added (in version 0.12.4). However, esbuild supports reading from multiple tsconfig.json files within a single build, which opens up the possibility that different files in the build have different language targets configured. There isn't really any reason to do this and it can lead to unexpected results. So with this release, the target setting in tsconfig.json will no longer affect esbuild's own target setting. You will have to use esbuild's own target setting instead (which is a single, global value).

  • TypeScript's jsx setting no longer causes esbuild to preserve JSX syntax (#​2634)

    TypeScript has a setting called jsx that controls how to transform JSX into JS. The tool-agnostic transform is called react, and the React-specific transform is called react-jsx (or react-jsxdev). There is also a setting called preserve which indicates JSX should be passed through untransformed. Previously people would run esbuild with "jsx": "preserve" in their tsconfig.json files and then be surprised when esbuild preserved their JSX. So with this release, esbuild will now ignore "jsx": "preserve" in tsconfig.json files. If you want to preserve JSX syntax with esbuild, you now have to use --jsx=preserve.

    Note: Some people have suggested that esbuild's equivalent jsx setting override the one in tsconfig.json. However, some projects need to legitimately have different files within the same build use different transforms (i.e. react vs. react-jsx) and having esbuild's global jsx setting override tsconfig.json would prevent this from working. This release ignores "jsx": "preserve" but still allows other jsx values in tsconfig.json files to override esbuild's global jsx setting to keep the ability for multiple files within the same build to use different transforms.

  • useDefineForClassFields behavior has changed (#​2584, #​2993)

    Class fields in TypeScript look like this (x is a class field):

    class Foo {
      x = 123
    }

    TypeScript has legacy behavior that uses assignment semantics instead of define semantics for class fields when useDefineForClassFields is enabled (in which case class fields in TypeScript behave differently than they do in JavaScript, which is arguably "wrong").

    This legacy behavior exists because TypeScript added class fields to TypeScript before they were added to JavaScript. The TypeScript team decided to go with assignment semantics and shipped their implementation. Much later on TC39 decided to go with define semantics for class fields in JavaScript instead. This behaves differently if the base class has a setter with the same name:

    class Base {
      set x(_) {
        console.log('x:', _)
      }
    }
    
    // useDefineForClassFields: false
    class AssignSemantics extends Base {
      constructor() {
        super()
        this.x = 123
      }
    }
    
    // useDefineForClassFields: true
    class DefineSemantics extends Base {
      constructor() {
        super()
        Object.defineProperty(this, 'x', { value: 123 })
      }
    }
    
    console.log(
      new AssignSemantics().x, // Calls the setter
      new DefineSemantics().x // Doesn't call the setter
    )

    When you run tsc, the value of useDefineForClassFields defaults to false when it's not specified and the target in tsconfig.json is present but earlier than ES2022. This sort of makes sense because the class field language feature was added in ES2022, so before ES2022 class fields didn't exist (and thus TypeScript's legacy behavior is active). However, TypeScript's target setting currently defaults to ES3 which unfortunately means that the useDefineForClassFields setting currently defaults to false (i.e. to "wrong"). In other words if you run tsc with all default settings, class fields will behave incorrectly.

    Previously esbuild tried to do what tsc did. That meant esbuild's version of useDefineForClassFields was false by default, and was also false if esbuild's --target= was present but earlier than es2022. However, TypeScript's legacy class field behavior is becoming increasingly irrelevant and people who expect class fields in TypeScript to work like they do in JavaScript are confused when they use esbuild with default settings. It's also confusing that the behavior of class fields would change if you changed the language target (even though that's exactly how TypeScript works).

    So with this release, esbuild will now only use the information in tsconfig.json to determine whether useDefineForClassFields is true or not. Specifically useDefineForClassFields will be respected if present, otherwise it will be false if target is present in tsconfig.json and is ES2021 or earlier, otherwise it will be true. Targets passed to esbuild's --target= setting will no longer affect useDefineForClassFields.

    Note that this means different directories in your build can have different values for this setting since esbuild allows different directories to have different tsconfig.json files within the same build. This should let you migrate your code one directory at a time without esbuild's --target= setting affecting the semantics of your code.

  • Add support for verbatimModuleSyntax from TypeScript 5.0

    TypeScript 5.0 added a new option called verbatimModuleSyntax that deprecates and replaces two older options, preserveValueImports and importsNotUsedAsValues. Setting verbatimModuleSyntax to true in tsconfig.json tells esbuild to not drop unused import statements. Specifically esbuild now treats "verbatimModuleSyntax": true as if you had specified both "preserveValueImports": true and "importsNotUsedAsValues": "preserve".

  • Add multiple inheritance for tsconfig.json from TypeScript 5.0

    TypeScript 5.0 now allows multiple inheritance for tsconfig.json files. You can now pass an array of filenames via the extends parameter and your tsconfig.json will start off containing properties from all of those configuration files, in order. This release of esbuild adds support for this new TypeScript feature.

  • Remove support for moduleSuffixes (#​2395)

    The community has requested that esbuild remove support for TypeScript's moduleSuffixes feature, so it has been removed in this release. Instead you can use esbuild's --resolve-extensions= feature to select which module suffix you want to build with.

  • Apply --tsconfig= overrides to stdin and virtual files (#​385, #​2543)

    When you override esbuild's automatic tsconfig.json file detection with --tsconfig= to pass a specific tsconfig.json file, esbuild previously didn't apply these settings to source code passed via the stdin API option or to TypeScript files from plugins that weren't in the file namespace. This release changes esbuild's behavior so that settings from tsconfig.json also apply to these source code files as well.

  • Support --tsconfig-raw= in build API calls (#​943, #​2440)

    Previously if you wanted to override esbuild's automatic tsconfig.json file detection, you had to create a new tsconfig.json file and pass the file name to esbuild via the --tsconfig= flag. With this release, you can now optionally use --tsconfig-raw= instead to pass the contents of tsconfig.json to esbuild directly instead of passing the file name. For example, you can now use --tsconfig-raw={"compilerOptions":{"experimentalDecorators":true}} to enable TypeScript experimental decorators directly using a command-line flag (assuming you escape the quotes correctly using your current shell's quoting rules). The --tsconfig-raw= flag previously only worked with transform API calls but with this release, it now works with build API calls too.

  • Ignore all tsconfig.json files in node_modules (#​276, #​2386)

    This changes esbuild's behavior that applies tsconfig.json to all files in the subtree of the directory containing tsconfig.json. In version 0.12.7, esbuild started ignoring tsconfig.json files inside node_modules folders. The rationale is that people typically do this by mistake and that doing this intentionally is a rare use case that doesn't need to be supported. However, this change only applied to certain syntax-specific settings (e.g. jsxFactory) but did not apply to path resolution settings (e.g. paths). With this release, esbuild will now ignore all tsconfig.json files in node_modules instead of only ignoring certain settings.

  • Ignore tsconfig.json when resolving paths within node_modules (#​2481)

    Previously fields in tsconfig.json related to path resolution (e.g. paths) were respected for all files in the subtree containing that tsconfig.json file, even within a nested node_modules subdirectory. This meant that a project's paths settings could potentially affect any bundled packages. With this release, esbuild will no longer use tsconfig.json settings during path resolution inside nested node_modules subdirectories.

  • Prefer .js over .ts within node_modules (#​3019)

    The default list of implicit extensions that esbuild will try appending to import paths contains .ts before .js. This makes it possible to bundle TypeScript projects that reference other files in the project using extension-less imports (e.g. ./some-file to load ./some-file.ts instead of ./some-file.js). However, this behavior is undesirable within node_modules directories. Some package authors publish both their original TypeScript code and their compiled JavaScript code side-by-side. In these cases, esbuild should arguably be using the compiled JavaScript files instead of the original TypeScript files because the TypeScript compilation settings for files within the package should be determined by the package author, not the user of esbuild. So with this release, esbuild will now prefer implicit .js extensions over .ts when searching for import paths within node_modules.

  These changes are intended to improve esbuild's compatibility with tsc and reduce the number of unfortunate behaviors regarding tsconfig.json and esbuild.

• Add a workaround for bugs in Safari 16.2 and earlier (#​3072)

  Safari's JavaScript parser had a bug (which has now been fixed) where at least something about unary/binary operators nested inside default arguments nested inside either a function or class expression was incorrectly considered a syntax error if that expression was the target of a property assignment. Here are some examples that trigger this Safari bug:

  ❱ x(function (y = -1) {}.z = 2)
  SyntaxError: Left hand side of operator '=' must be a reference.
  
  ❱ x(class { f(y = -1) {} }.z = 2)
  SyntaxError: Left hand side of operator '=' must be a reference.
  

  It's not clear what the exact conditions are that trigger this bug. However, a workaround for this bug appears to be to post-process your JavaScript to wrap any in function and class declarations that are the direct target of a property access expression in parentheses. That's the workaround that UglifyJS applies for this issue: mishoo/UglifyJS#​2056. So that's what esbuild now does starting with this release:

  // Original code
  x(function (y = -1) {}.z = 2, class { f(y = -1) {} }.z = 2)
  
  // Old output (with --minify --target=safari16.2)
  x(function(c=-1){}.z=2,class{f(c=-1){}}.z=2);
  
  // New output (with --minify --target=safari16.2)
  x((function(c=-1){}).z=2,(class{f(c=-1){}}).z=2);

  This fix is not enabled by default. It's only enabled when --target= contains Safari 16.2 or earlier, such as with --target=safari16.2. You can also explicitly enable or disable this specific transform (called function-or-class-property-access) with --supported:function-or-class-property-access=false.

• Fix esbuild's TypeScript type declarations to forbid unknown properties (#​3089)

  Version 0.17.0 of esbuild introduced a specific form of function overloads in the TypeScript type definitions for esbuild's API calls that looks like this:

  interface TransformOptions {
    legalComments?: 'none' | 'inline' | 'eof' | 'external'
  }
  
  interface TransformResult<ProvidedOptions extends TransformOptions = TransformOptions> {
    legalComments: string | (ProvidedOptions['legalComments'] extends 'external' ? never : undefined)
  }
  
  declare function transformSync<ProvidedOptions extends TransformOptions>(input: string, options?: ProvidedOptions): TransformResult<ProvidedOptions>
  declare function transformSync(input: string, options?: TransformOptions): TransformResult

  This more accurately reflects how esbuild's JavaScript API behaves. The result object returned by transformSync only has the legalComments property if you pass legalComments: 'external':

  // These have type "string | undefined"
  transformSync('').legalComments
  transformSync('', { legalComments: 'eof' }).legalComments
  
  // This has type "string"
  transformSync('', { legalComments: 'external' }).legalComments

  However, this form of function overloads unfortunately allows typos (e.g. egalComments) to pass the type checker without generating an error as TypeScript allows all objects with unknown properties to extend TransformOptions. These typos result in esbuild's API throwing an error at run-time.

  To prevent typos during type checking, esbuild's TypeScript type definitions will now use a different form that looks like this:

  type SameShape<Out, In extends Out> = In & { [Key in Exclude<keyof In, keyof Out>]: never }
  
  interface TransformOptions {
    legalComments?: 'none' | 'inline' | 'eof' | 'external'
  }
  
  interface TransformResult<ProvidedOptions extends TransformOptions = TransformOptions> {
    legalComments: string | (ProvidedOptions['legalComments'] extends 'external' ? never : undefined)
  }
  
  declare function transformSync<T extends TransformOptions>(input: string, options?: SameShape<TransformOptions, T>): TransformResult<T>

  This change should hopefully not affect correct code. It should hopefully introduce type errors only for incorrect code.

• Fix CSS nesting transform for pseudo-elements (#​3119)

  This release fixes esbuild's CSS nesting transform for pseudo-elements (e.g. ::before and ::after). The CSS nesting specification says that the nesting selector does not work with pseudo-elements. This can be seen in the example below: esbuild does not carry the parent pseudo-element ::before through the nesting selector &. However, that doesn't apply to pseudo-elements that are within the same selector. Previously esbuild had a bug where it considered pseudo-elements in both locations as invalid. This release changes esbuild to only consider those from the parent selector invalid, which should align with the specification:

  /* Original code */
  a, b::before {
    &.c, &::after {
      content: 'd';
    }
  }
  
  /* Old output (with --target=chrome90) */
  a:is(.c, ::after) {
    content: "d";
  }
  
  /* New output (with --target=chrome90) */
  a.c,
  a::after {
    content: "d";
  }

• Forbid & before a type selector in nested CSS

  The people behind the work-in-progress CSS nesting specification have very recently decided to forbid nested CSS that looks like &div. You will have to use either div& or &:is(div) instead. This release of esbuild has been updated to take this new change into consideration. Doing this now generates a warning. The suggested fix is slightly different depending on where in the overall selector it happened:

  ▲ [WARNING] Cannot use type selector "input" directly after nesting selector "&" [css-syntax-error]
  
      example.css:2:3:
        2 │   &input {
          │    ~~~~~
          ╵    :is(input)
  
    CSS nesting syntax does not allow the "&" selector to come before a type selector. You can wrap
    this selector in ":is()" as a workaround. This restriction exists to avoid problems with SASS
    nesting, where the same syntax means something very different that has no equivalent in real CSS
    (appending a suffix to the parent selector).
  
  ▲ [WARNING] Cannot use type selector "input" directly after nesting selector "&" [css-syntax-error]
  
      example.css:6:8:
        6 │   .form &input {
          │         ~~~~~~
          ╵         input&
  
    CSS nesting syntax does not allow the "&" selector to come before a type selector. You can move
    the "&" to the end of this selector as a workaround. This restriction exists to avoid problems
    with SASS nesting, where the same syntax means something very different that has no equivalent in
    real CSS (appending a suffix to the parent selector).