@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.

Skipping compilation for runtime JS

Plain JavaScript files (.js, .mjs, .cjs, .es, .es6) that Node can already execute are passed through without an SWC transform, which speeds up startup. A file is still transformed when it needs to be — it contains JSX, it uses ESM syntax under CommonJS output, or an .swcrc is in effect.

Known caveats (kept intentionally, for speed):

• A tsconfig.json paths alias imported via dynamic import('@alias/…') in a passed-through .js file is not rewritten, so the alias will not resolve. Static import/require are unaffected. Use .ts/.mts (or a static import) if you rely on alias resolution here.
• Dynamically import()-ing a CommonJS module from a passed-through .js file yields a native module namespace rather than SWC's interop shape (ns.default instead of ns).