| Usage: kotlinc-js <options> <source files> |
| where advanced options include: |
| -Xenable-extension-functions-in-externals |
| Enable extension function members in external interfaces. |
| -Xenable-implementing-interfaces-from-typescript |
| Enable exporting of Kotlin interfaces to implement them from JavaScript/TypeScript. |
| -Xenable-suspend-function-exporting |
| Enable exporting suspend functions to JavaScript/TypeScript. |
| -Xes-arrow-functions Use ES2015 arrow functions in the JavaScript code generated for Kotlin lambdas. Enabled by default in case of ES2015 target usage |
| -Xes-classes Let generated JavaScript code use ES2015 classes. Enabled by default in case of ES2015 target usage |
| -Xes-generators Enable ES2015 generator functions usage inside the compiled code. Enabled by default in case of ES2015 target usage |
| -Xes-long-as-bigint Compile Long values as ES2020 bigint instead of object. |
| -Xgenerate-polyfills Generate polyfills for features from the ES6+ standards. |
| -Xir-build-cache Use the compiler to build the cache. |
| -Xir-generate-inline-anonymous-functions |
| Lambda expressions that capture values are translated into in-line anonymous JavaScript functions. |
| -Xir-keep Comma-separated list of fully qualified names not to be eliminated by DCE (if it can be reached), and for which to keep non-minified names. |
| -Xir-minimized-member-names Minimize the names of members. |
| -Xir-per-file Generate one .js file per source file. |
| -Xir-per-module Generate one .js file per module. |
| -Xir-safe-external-boolean Wrap access to external 'Boolean' properties with an explicit conversion to 'Boolean'. |
| -Xir-safe-external-boolean-diagnostic={log|exception} |
| Enable runtime diagnostics when accessing external 'Boolean' properties. |
| -Xoptimize-generated-js Perform additional optimizations on the generated JS code. |
| -Xplatform-arguments-in-main-function |
| JS expression that will be executed in runtime and be put as an Array<String> parameter of the main function |
| -Xir-dce-dump-reachability-info-to-file=<path> |
| Dump reachability information collected about declarations while performing DCE to a file. The format will be chosen automatically based on the file extension. Supported output formats include JSON for .json, a JS const initialized with a plain object containing information for .js, and plain text for all other file types. |
| -Xir-dump-declaration-ir-sizes-to-file=<path> |
| Dump the IR size of each declaration into a file. The format will be chosen automatically depending on the file extension. Supported output formats include JSON for .json, a JS const initialized with a plain object containing information for .js, and plain text for all other file types. |
| -Xwasm Use the WebAssembly compiler backend. |
| -Xwasm-debug-friendly Avoid optimizations that can break debugging. |
| -Xwasm-debug-info Add debug info to the compiled WebAssembly module. |
| -Xwasm-debugger-custom-formatters |
| Generates devtools custom formatters (https://firefox-source-docs.mozilla.org/devtools-user/custom_formatters) for Kotlin/Wasm values |
| -Xwasm-enable-array-range-checks |
| Turn on range checks for array access functions. |
| -Xwasm-enable-asserts Turn on asserts. |
| -Xwasm-generate-closed-world-multimodule |
| Compile modules in multi-module closed-world mode using module passed in `-include` argument as main module |
| -Xwasm-generate-dwarf Generate DWARF debug information. |
| -Xwasm-generate-wat Generate a .wat file. |
| -Xwasm-included-module-only Compile only a module passed using `-include` option. |
| -Xwasm-internal-local-variable-prefix |
| Prefix to use for internally generated local variables. |
| -Xwasm-kclass-fqn Enable support for 'KClass.qualifiedName'. |
| -Xwasm-no-jstag Don't use WebAssembly.JSTag for throwing and catching exceptions |
| -Xwasm-source-map-include-mappings-from-unavailable-sources |
| Insert source mappings from libraries even if their sources are unavailable on the end-user machine. |
| -Xwasm-target Set up the Wasm target (wasm-js or wasm-wasi). |
| -Xwasm-use-new-exception-proposal |
| Use an updated version of the exception proposal with try_table. |
| -Xwasm-use-traps-instead-of-exceptions |
| Use traps instead of throwing exceptions. |
| -Xcache-directory=<path> Path to the cache directory. |
| -Xfake-override-validator Enable the IR fake override validator. |
| -Xfriend-modules=<path> Paths to friend modules. |
| -Xfriend-modules-disabled Disable internal declaration export. |
| -Xgenerate-dts Generate a TypeScript declaration .d.ts file alongside the JS file. |
| -Xinclude=<path> Path to an intermediate library that should be processed in the same manner as source files. |
| -Xir-dce Perform experimental dead code elimination. |
| -Xir-dce-print-reachability-info |
| Print reachability information about declarations to 'stdout' while performing DCE. |
| -Xir-dce-runtime-diagnostic={log|exception} |
| Enable runtime diagnostics instead of removing declarations when performing DCE. |
| -Xir-module-name=<name> Specify the name of the compilation module for the IR backend. |
| -Xir-per-module-output-name Add a custom output name to the split .js files. |
| -Xir-produce-js Generate a JS file using the IR backend. |
| -Xir-produce-klib-dir Generate an unpacked klib into the parent directory of the output JS file. |
| -Xir-produce-klib-file Generate a packed klib into the directory specified by '-ir-output-dir'. |
| -Xir-property-lazy-initialization |
| Perform lazy initialization for properties. |
| -Xstrict-implicit-export-types Generate strict types for implicitly exported entities inside d.ts files. |
| -Xklib-abi-version=<version> Specify the custom ABI version to be written in KLIB. This option is intended only for tests. |
| Warning: This option does not affect KLIB ABI. Neither allows it making a KLIB backward-compatible with older ABI versions. |
| The only observable effect is that a custom ABI version is written to KLIB manifest file. |
| -Xklib-duplicated-unique-name-strategy={deny|allow-all-with-warning|allow-first-with-warning} |
| Klib dependencies usage strategy when multiple KLIBs has same `unique_name` property value. |
| -Xklib-enable-signature-clash-checks |
| Enable signature uniqueness checks. |
| -Xklib-ir-inliner={intra-module|full|disabled|default} |
| Set the mode of the experimental IR inliner on the first compilation stage. |
| - `intra-module` mode enforces inlining of the functions only from the compiled module |
| - `full` mode enforces inlining of all functions (from the compiled module and from all dependencies) |
| Warning: This mode will trigger setting the `pre-release` flag for the compiled library. |
| - `disabled` mode completely disables the IR inliner |
| - `default` mode lets the IR inliner run in `intra-module`, `full` or `disabled` mode based on the current language version |
| |
| -Xklib-normalize-absolute-path Normalize absolute paths in klibs. |
| -Xklib-relative-path-base Relativize all the paths stored in a klib using the given path prefixes. |
| The supplied prefixes should be absolute paths to the directories containing the source code files. |
| Note: The prefixes are applied in the same order as they are passed in this CLI argument. |
| -Xklib-zip-file-accessor-cache-limit |
| Maximum number of klibs that can be cached during compilation. Default is 64. |
| -Xpartial-linkage={enable|disable} |
| This option is deprecated and will be deleted in future versions. |
| The partial linkage engine is always turned on. |
| If you would like to adjust the compile-time log level for partial linkage, use -Xpartial-linkage-loglevel. |
| -Xpartial-linkage-loglevel={silent|info|warning|error} |
| Define the compile-time log level for partial linkage. |
| -Xskip-library-special-compatibility-checks |
| Skip library compatibility checks for stdlib and kotlin.test library. |
| -Xallow-any-scripts-in-source-roots |
| Allow compiling scripts along with regular Kotlin sources. |
| -Xallow-condition-implies-returns-contracts |
| Allow contracts that specify a limited conditional returns postcondition. |
| -Xallow-contracts-on-more-functions |
| Allow contracts on some operators and accessors, and allow checks for erased types. |
| -Xallow-holdsin-contract Allow contracts that specify a condition that holds true inside a lambda argument. |
| -Xallow-kotlin-package Allow compiling code in the 'kotlin' package, and allow not requiring 'kotlin.stdlib' in 'module-info'. |
| -Xallow-reified-type-in-catch Allow 'catch' parameters to have reified types. |
| -Xallow-returns-result-of Allows to use `returnsResultOf()` in `contract {}` block of function body. This contract provides additional information for return value checker. Enabling this feature will force compiler to produce pre-release binaries, because this functions with this contract cannot be read correctly by Kotlin 2.3 and lower. |
| -Xannotation-default-target=first-only|first-only-warn|param-property |
| Change the default annotation targets for constructor properties: |
| -Xannotation-default-target=first-only: use the first of the following allowed targets: '@param:', '@property:', '@field:'; |
| -Xannotation-default-target=first-only-warn: same as first-only, and raise warnings when both '@param:' and either '@property:' or '@field:' are allowed; |
| -Xannotation-default-target=param-property: use '@param:' target if applicable, and also use the first of either '@property:' or '@field:'; |
| default: 'param-property' in language version 2.4+, 'first-only-warn' in language versions 2.2 & 2.3, 'first-only' in version 2.1 and before. |
| -Xannotation-target-all Enable experimental language support for @all: annotation use-site target. |
| -Xcheck-phase-conditions Check pre- and postconditions of IR lowering phases. |
| -Xcollection-literals Enable experimental language support for collection literals. |
| -Xcommon-sources=<path> Sources of the common module that need to be compiled together with this module in multiplatform mode. |
| They should be a subset of sources passed as free arguments. |
| -Xcompiler-plugin=<path1>,<path2>[=<optionName>=<value>,<optionName>=<value>] |
| Register a compiler plugin. |
| -Xcompiler-plugin-order=<pluginId1>><pluginId2> |
| Specify an execution order constraint for compiler plugins. |
| Order constraint can be specified using the 'pluginId' of compiler plugins. |
| The first specified plugin will be executed before the second plugin. |
| Multiple constraints can be specified by repeating this option. Cycles in constraints will cause an error. |
| -Xconsistent-data-class-copy-visibility |
| The effect of this compiler flag is the same as applying @ConsistentCopyVisibility annotation to all data classes in the module. See https://youtrack.jetbrains.com/issue/KT-11914 |
| -Xcontext-parameters Enable experimental context parameters. |
| -Xcontext-receivers Enable experimental context receivers. |
| -Xcontext-sensitive-resolution Enable experimental context-sensitive resolution. |
| -Xdata-flow-based-exhaustiveness |
| Enable `when` exhaustiveness improvements that rely on data-flow analysis. |
| -Xdetailed-perf Enable more detailed performance statistics (Experimental). |
| For Native, the performance report includes execution time and lines processed per second for every individual lowering. |
| For WASM and JS, the performance report includes execution time and lines per second for each lowering of the first stage of compilation. |
| -Xdirect-java-actualization Enable experimental direct Java actualization support. |
| -Xdisable-default-scripting-plugin |
| Don't enable the scripting plugin by default. |
| -Xdisable-phases Disable backend phases. |
| -Xdont-sort-source-files Disable automatic sorting of source files. |
| -Xdont-warn-on-error-suppression |
| Don't report warnings when errors are suppressed. This only affects K2. |
| -Xdump-directory Dump the backend state into this directory. |
| -Xdump-fqname Dump the declaration with the given FqName. |
| -Xdump-perf=<path> Dump detailed performance statistics to the specified file in plain text, JSON or markdown format (it's detected by the file's extension). |
| Also, it supports the placeholder `*` and directory for generating file names based on the module being compiled and the current time stamp. |
| Example: `path/to/dir/*.log` creates logs like `path/to/dir/my-module_2025-06-20-12-22-32.log` in plain text format, `path/to/dir/` creates logs like `path/to/dir/my-log_2025-06-20-12-22-32.json`. |
| -Xenable-incremental-compilation |
| Enable incremental compilation. |
| -Xexpect-actual-classes 'expect'/'actual' classes (including interfaces, objects, annotations, enums, and 'actual' typealiases) are in Beta. |
| Kotlin reports a warning every time you use one of them. You can use this flag to mute the warning. |
| -Xexplicit-api={strict|warning|disable} |
| Force the compiler to report errors on all public API declarations without an explicit visibility or a return type. |
| Use the 'warning' level to issue warnings instead of errors. |
| -Xexplicit-backing-fields Enable experimental language support for explicit backing fields. |
| -Xexplicit-context-arguments Enable explicit passing of context arguments using named argument syntax. |
| -Xfragment-dependency=<fragment name>:<path> |
| Declare common klib dependencies for the specific fragment. |
| This argument is required for any HMPP module except the platform leaf module: it takes dependencies from -cp/-libraries. |
| The argument should be used only if the new compilation scheme is enabled with -Xseparate-kmp-compilation |
| |
| -Xfragment-friend-dependency=<fragment name>:<path> |
| Declare common klib friend dependencies for the specific fragment. |
| This argument can be specified for any HMPP module except the platform leaf module: it takes dependencies from the platform specific friend module arguments. |
| The argument should be used only if the new compilation scheme is enabled with -Xseparate-kmp-compilation |
| |
| -Xfragment-refines=<fromModuleName>:<onModuleName> |
| Declare that <fromModuleName> refines <onModuleName> with the dependsOn/refines relation. |
| -Xfragment-sources=<fragment name>:<path> |
| Add sources to a specific fragment of a multiplatform compilation. |
| -Xfragments=<fragment name> Declare all known fragments of a multiplatform compilation. |
| -Xheader-mode Enable header compilation mode. |
| In this mode, the compiler produces class files that only contain the 'skeleton' of the classes to be |
| compiled but the method bodies of all the implementations are empty. This is used to speed up parallel compilation |
| build systems where header libraries can be used to replace downstream dependencies for which we only need to |
| see the type names and method signatures required to compile a given translation unit. Inline functions are still kept |
| with bodies. |
| -Xheader-mode-type={any|compilation} |
| Generates output based on what it is used for: |
| -Xheader-mode-type=compilation: Skips the IR generation for modules that don't have inline functions. |
| -Xheader-mode-type=any: Can be used for any downstream dependency which doesn't require linking. |
| -Xignore-const-optimization-errors |
| Ignore all compilation exceptions while optimizing some constant expressions. |
| -Xinline-classes Enable experimental inline classes. |
| -Xintellij-plugin-root=<path> Path to 'kotlin-compiler.jar' or the directory where the IntelliJ IDEA configuration files can be found. |
| -Xintrinsic-const-evaluation Enables `IntrinsicConstEvaluation` language feature.` |
| -Xlist-phases List backend phases. |
| -Xlocal-type-aliases Enable experimental language support for local type aliases. |
| -Xmetadata-klib Produce a klib that only contains the metadata of declarations. |
| -Xmetadata-version Change the metadata version of the generated binary files. |
| -Xmulti-dollar-interpolation Enable experimental multi-dollar interpolation. |
| -Xmulti-platform Enable language support for multiplatform projects. |
| -Xname-based-destructuring=only-syntax|name-mismatch|complete |
| Enables the following destructuring features: |
| -Xname-based-destructuring=only-syntax: Enables syntax for positional destructuring with square brackets and the full form of name-based destructuring with parentheses; |
| -Xname-based-destructuring=name-mismatch: Reports warnings when short form positional destructuring of data classes uses names that don't match the property names; |
| -Xname-based-destructuring=complete: Enables short-form name-based destructuring with parentheses; |
| -Xnested-type-aliases Enable experimental language support for nested type aliases. |
| -Xnew-inference Enable the new experimental generic type inference algorithm. |
| -Xno-check-actual Do not check for the presence of the 'actual' modifier in multiplatform projects. |
| -Xno-inline Disable method inlining. |
| -Xnon-local-break-continue Enable experimental non-local break and continue. |
| -Xphases-to-dump Dump the backend's state both before and after these phases. |
| -Xphases-to-dump-after Dump the backend's state after these phases. |
| -Xphases-to-dump-before Dump the backend's state before these phases. |
| -Xphases-to-validate Validate the backend's state both before and after these phases. |
| -Xphases-to-validate-after Validate the backend's state after these phases. |
| -Xphases-to-validate-before Validate the backend's state before these phases. |
| -Xplugin=<path> Load plugins from the given classpath. |
| -Xprint-configuration Print compiler configuration. |
| -Xprofile-phases Profile backend phases. |
| -Xrender-internal-diagnostic-names |
| Render the internal names of warnings and errors. |
| -Xrepl Run Kotlin REPL (deprecated) |
| -Xreport-all-warnings Report all warnings even if errors are found. |
| -Xreport-output-files Report the source-to-output file mapping. |
| -Xreport-perf Report detailed performance statistics. |
| -Xreturn-value-checker={check|full|disable} |
| Set improved unused return value checker mode. Use 'check' to run checker only and use 'full' to also enable automatic annotation insertion. |
| -Xseparate-kmp-compilation Enables the separated compilation scheme, in which common source sets are analyzed against their own dependencies |
| -Xskip-metadata-version-check Allow loading classes with bad metadata versions and pre-release classes. |
| -Xskip-prerelease-check Allow loading pre-release classes. |
| -Xstdlib-compilation Enables special features which are relevant only for stdlib compilation. |
| -Xsuppress-api-version-greater-than-language-version-error |
| Suppress error about API version greater than language version. |
| Warning: This is temporary solution (see KT-63712) intended to be used only for stdlib build. |
| -Xsuppress-version-warnings Suppress warnings about outdated, inconsistent, or experimental language or API versions. |
| -Xsuppress-warning=<WARNING_NAME> |
| Suppress specified warning module-wide. This option is deprecated in favor of "-Xwarning-level" flag |
| -Xunrestricted-builder-inference |
| Eliminate builder inference restrictions, for example by allowing type variables to be returned from builder inference calls. |
| -Xuse-fir-experimental-checkers |
| Enable experimental frontend IR checkers that are not yet ready for production. |
| -Xuse-fir-ic Compile using frontend IR internal incremental compilation. |
| Warning: This feature is not yet production-ready. |
| -Xuse-fir-lt Compile using the LightTree parser with the frontend IR. |
| -Xverbose-phases Be verbose while performing the given backend phases. |
| -Xverify-ir={none|warning|error} |
| IR verification mode (no verification by default). |
| -Xverify-ir-nested-offsets Check that offsets of nested IR elements conform to offsets of their containers. Only has effect if '-Xverify-ir' is not 'none'. |
| -Xverify-ir-visibility Check for visibility violations in IR when validating it before running any lowerings. Only has effect if '-Xverify-ir' is not 'none'. |
| -Xwarning-level=<WARNING_NAME>:(error|warning|disabled) |
| Set the severity of the given warning. |
| - `error` level raises the severity of a warning to error level (similar to -Werror but more granular) |
| - `disabled` level suppresses reporting of a warning (similar to -nowarn but more granular) |
| - `warning` level overrides -nowarn and -Werror for this specific warning (the warning will be reported/won't be considered as an error) |
| -Xwhen-guards Enable experimental language support for when guards. |
| |
| Advanced options are non-standard and may be changed or removed without any notice. |
| OK |
