Function registerExtensions

src/index.ts:1559–1595

* Register the extensions to support when importing files.

(
  preferTsExts: boolean | null | undefined,
  extensions: string[],
  service: Service,
  originalJsHandler: (m: NodeModule, filename: string) => any
)

 * Register the extensions to support when importing files.
 */
function registerExtensions(
  preferTsExts: boolean | null | undefined,
  extensions: string[],
  service: Service,
  originalJsHandler: (m: NodeModule, filename: string) => any
) {
  const exts = new Set(extensions);
  // Can't add these extensions cuz would allow omitting file extension; node requires ext for .cjs and .mjs
  // Unless they're already registered by something else (nyc does this):
  // then we *must* hook them or else our transformer will not be called.
  for (const cannotAdd of ['.mts', '.cts', '.mjs', '.cjs']) {
    if (exts.has(cannotAdd) && !hasOwnProperty(require.extensions, cannotAdd)) {
      // Unrecognized file exts can be transformed via the `.js` handler.
      exts.add('.js');
      exts.delete(cannotAdd);
    }
  }

  // Register new extensions.
  for (const ext of exts) {
    registerExtension(ext, service, originalJsHandler);
  }

  if (preferTsExts) {
    const preferredExtensions = new Set([
      ...exts,
      ...Object.keys(require.extensions),
    ]);

    // Re-sort iteration order of Object.keys()
    for (const ext of preferredExtensions) {
      const old = Object.getOwnPropertyDescriptor(require.extensions, ext);
      delete require.extensions[ext];
      Object.defineProperty(require.extensions, ext, old!);
    }
  }
}

/**
 * Register the extension for node.