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Modules

SWC can transpile your code using ES Modules to CommonJS or UMD/AMD. By default, module statements will remain untouched.

CommonJS

To emit a CommonJS module, change the type in .swcrc:

{
"module": {
"type": "commonjs",
// These are defaults.
"strict": false,
"strictMode": true,
"lazy": false,
"noInterop": false
}
}

ES6

To emit a ES6 module, change the type in .swcrc:

{
"module": {
"type": "es6",
// These are defaults.
"strict": false,
"strictMode": true,
"lazy": false,
"noInterop": false
}
}

AMD

To emit an AMD module, change the type in .swcrc:

{
"module": {
"type": "amd",
// Optional. If specified, swc emits named AMD module.
"moduleId": "foo",
// These are defaults.
"strict": false,
"strictMode": true,
"lazy": false,
"noInterop": false
}
}

UMD

To emit an UMD module, change the type in .swcrc:

{
"module": {
"type": "umd",
"globals": {},
// These are defaults.
"strict": false,
"strictMode": true,
"lazy": false,
"noInterop": false
}
}

Shared Options

These options are shared by commonjs / es6 / umd / amd inside .swcrc:

{
"module": {
// You can specify "commonjs", "es6", "amd", "umd"
"type": "commonjs",
"strict": false,
"strictMode": true,
"lazy": false,
"noInterop": false,
"ignoreDynamic": false
}
}

strict

Defaults to false. By default, when using exports with SWC, a non-enumerable __esModule property is exported. In some cases, this property is used to determine if the import is the default export or if it contains the default export.

To prevent the __esModule property from being exported, you can set the strict option to true.

strictMode

Defaults to true. If true, swc emits 'use strict' directive.

lazy

Defaults to false. This option changes Babel's compiled import statements to be lazily evaluated when their imported bindings are used for the first time. This can improve the initial load time of your module because evaluating dependencies upfront is sometimes entirely unnecessary. This is especially the case when implementing a library module.

The value of lazy has a few possible effects:

  • false - No lazy initialization of any imported module.
  • true - Do not lazy-initialize local ./foo imports, but lazy-init foo dependencies. Local paths are much more likely to have circular dependencies, which may break if loaded lazily, so they are not lazy by default, whereas dependencies between independent modules are rarely cyclical.
  • Array<string> - Lazy-initialize all imports with source matching one of the given strings.

The two cases where imports can never be lazy are:

  • import "foo"; Side-effect imports are automatically non-lazy since their very existence means that there is no binding to later kick-off initialization.
  • export from "foo" Re-exporting all names requires up-front execution because otherwise there is no way to know what names need to be exported.

noInterop

Defaults to false. By default, when using exports with swc a non-enumerable __esModule property is exported. This property is then used to determine if the import is the default export or if it contains the default export.

In cases where the auto-unwrapping of default is not needed, you can set the noInterop option to true to avoid the usage of the interopRequireDefault helper (shown in inline form above).

ignoreDynamic

If set to true, dynamic imports will be preserved.