Clear and concise description of the problem

https://nodejs.org/api/packages.html#extensions-in-subpaths

That mentions import maps and adding .js extensions to your package exports. There currently is no config option to enable this in tsdown. I was able to add this myself by having a customExports callback:

exports: {
    devExports: true,
    customExports(exports) {
      return Object.fromEntries(
        Object.entries(exports).map(([key, value]) => {
          if (key === '.' || /\.[^/]+$/.test(key)) {
            return [key, value];
          }

          return [`${key}.js`, value];
        })
      );
    }
  },

Suggested solution

Please expand the exports config option to support this.

Alternative

Write your own customExports callback as shown above.

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guide.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.