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@swc-node/register

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Usage

const { register } = require('@swc-node/register/register')

register({
  ...
})

CLI

node -r @swc-node/register index.ts

Mocha

mocha --require @swc-node/register --watch-extensions ts,tsx "test/**/*.{ts,tsx}" [...args]

ava

// package.json

{
  "ava": {
    "extensions": ["ts", "tsx"],
    "require": ["@swc-node/register"],
    "files": ["packages/**/*.spec.{ts,tsx}"]
  }
}

Read tsconfig.json

set SWC_NODE_PROJECT or TS_NODE_PROJECT env:

SWC_NODE_PROJECT=./tsconfig.test.json mocha --require @swc-node/register --watch-extensions ts,tsx "test/**/*.{ts,tsx}" [...args]

@swc-node/register respect the following option in tsconfig:

extends

@swc-node/register respect the extends key in tsconfig.json, and use the merged values.

compilerOptions.target

switch (target) {
  case ts.ScriptTarget.ES3:
    return 'es3'
  case ts.ScriptTarget.ES5:
    return 'es5'
  case ts.ScriptTarget.ES2015:
    return 'es2015'
  case ts.ScriptTarget.ES2016:
    return 'es2016'
  case ts.ScriptTarget.ES2017:
    return 'es2017'
  case ts.ScriptTarget.ES2018:
    return 'es2018'
  case ts.ScriptTarget.ES2019:
    return 'es2019'
  case ts.ScriptTarget.ES2020:
  case ts.ScriptTarget.ES2021:
  case ts.ScriptTarget.ES2022:
  case ts.ScriptTarget.ESNext:
  case ts.ScriptTarget.Latest:
    return 'es2020'
  case ts.ScriptTarget.JSON:
    return 'es5'
}

compilerOptions.jsx

If filename endsWith .jsx or .tsx, always set the jsx: true in swc config regards the jsx option in tsconfig. If filename not endsWith .jsx or .tsx, set the jsx: Boolean(tsconfig.compilerOptions.jsx) in swc config.

compilerOptions.module

notes, if compilerOptions.module higher than es2020, the dynamicImport in swc config will be set to true.

switch (moduleKind) {
  case ts.ModuleKind.CommonJS:
    return 'commonjs'
  case ts.ModuleKind.UMD:
    return 'umd'
  case ts.ModuleKind.AMD:
    return 'amd'
  case ts.ModuleKind.ES2015:
  case ts.ModuleKind.ES2020:
  case ts.ModuleKind.ESNext:
  case ts.ModuleKind.None:
    return 'es6'
  case ts.ModuleKind.System:
    throw new TypeError('Do not support system kind module')
}

compilerOptions.experimentalDecorators

Respect the boolean value in tsconfig.

compilerOptions.emitDecoratorMetadata

Respect the boolean value in tsconfig.

compilerOptions.esModuleInterop

Respect the boolean value in tsconfig.

include/exclude

TypeScript gives files list to @swc-node/register, if parse tsconfig.json failed or files list empty, @swc-node/register will transform all files which were required.

And if failed to parse tsconfig.json, @swc-node/register will print warning which contains failed reason.

Performance tuning

Transform cache

@swc-node/register now keeps a transform cache (memory + disk) keyed by source, filename, compiler options, and runtime versions.

Environment variables:

  • SWC_NODE_CACHE=0 disable cache.
  • SWC_NODE_CACHE_DIR=./path/to/cache choose disk cache directory.
  • SWC_NODE_CACHE_MEMORY_LIMIT=2000 max in-process transform entries.

Programmatic cache control:

const { clearTransformCache, getTransformCacheDirectory } = require('@swc-node/register/register')

// clear memory + disk (default)
clearTransformCache()

// clear only memory cache
clearTransformCache({ memory: true, disk: false })

// inspect resolved disk cache path
console.log(getTransformCacheDirectory())

Source map memory mode

Use SWC_NODE_SOURCE_MAP_MODE to tune source map memory behavior:

  • auto (default): inline maps when Node native source maps are enabled, otherwise map-store mode.
  • inline: inline data URL source maps only.
  • store: in-memory map store only (source-map-support path).
  • both: inline + store (highest memory use, mainly for compatibility/debug edge cases).
  • none: disable both inline/store map injection.