Allow loading config files in TypeScript format (#2709)

Author: davidjgoss

CHANGELOG.md

@@ -8,6 +8,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 Please see [CONTRIBUTING.md](./CONTRIBUTING.md) on how to contribute to Cucumber.
 
 ## [Unreleased]
+### Added
+- Allow loading config files in TypeScript format ([#2709](https://github.com/cucumber/cucumber-js/pull/2709))
+
 ### Changed
 - Compress report content with gzip before publishing ([#2687](https://github.com/cucumber/cucumber-js/pull/2687))
 

docs/configuration.md

@@ -71,11 +71,18 @@ module.exports = {
 
 (If you're wondering why the configuration sits within a "default" property, that's to allow for [Profiles](./profiles.md).)
 
-### Type checking
+### TypeScript
 
-If you want to type check your configuration, we export two types that can help with that:
-- `IProfiles` represents the dictionary of profile names to configuration objects exported for CommonJS
-- `IConfiguration` represents a single configuration object exported with named exports for ESM (`Partial<IConfiguration>` will be more useful in practise)
+You can also write your configuration file in TypeScript, with a `.ts`, `.mts` or `.cts` extension. These files are loaded with [Node.js built-in TypeScript support](https://nodejs.org/api/typescript.html), which has several caveats and limitations, mostly that your `tsconfig.json` won't be honoured and that you need to be explicit about type imports. Here's an example:
+
+```typescript
+import type { IConfiguration } from '@cucumber/cucumber'
+
+export default {
+  parallel: 2,
+  format: ['html:cucumber-report.html']
+} satisfies Partial<IConfiguration>
+```
 
 ## Options