ts-transform-default-export

ts-transform-default-export

A TypeScript transformer that converts a default export such as one of these:

export default function foo() {}
export default foo
export { foo as default }

to its CommonJS counterpart:

export = foo

When such a module is then transpiled to CommonJS or UMD, the export will become module.exports = foo, making the module consumable by require('foo') instead of require('foo').default.

Only files that match the files or include property of your tsconfig.json will be transformed. This is an intentional restriction to make it possible to control which files are processed.

Installation

npm install --save-dev ts-transform-default-export

Currently there is no native way to add a custom transformer to your TypeScript compilation pipeline. Instead, you have to use a third-party tool (TTypescript, ts-patch) or a plugin for your bundler. For concrete instructions refer to the docs of the tool of your choice.

The type of this transformer is program, the most common one. To transform the module file, add it to the before stage. To transform the emitted declaration file, add it to afterDeclarations.

Example tsconfig.json for TTypescript

{
  "compilerOptions": {
    "module": "CommonJS",
    "plugins": [{
      "transform": "ts-transform-default-export",
      "afterDeclarations": true,
      "keepOriginalExport": true // Transformer option
    }]
  },
  "include": ["src/index.ts"]
}

Options

keepOriginalExport: boolean

Whether to keep the original default export in the code when transforming it.

• When false (default):

  export default foo → export = foo

• When true:

  export default foo → export default foo; export = foo

allowNamedExports: boolean

Whether to throw when there are named exports in the module along with the default one. This is important because when a default export is converted to export =, named exports could get lost. For example, export { foo as default, bar } becomes exports.bar = bar; module.exports = foo, so bar is overwritten.

You can work around this by assigning the named exports to the default export's value if possible (foo.bar = bar; export { foo as default, bar }) and setting this option to true.

• When false (default):

  export { foo as default, bar } → throws an error

• When true (and keepOriginalExport is false):

  export { foo as default, bar } → export { bar }; export = foo

• When true (and keepOriginalExport is true):

  export { foo as default, bar } → export { foo as default, bar }; export = foo

License

ISC