Kotlin JavaScript to TypeScript Definition File

I'm looking to do something like this to share models between Android and JS. There is the ts-generator library, which takes jvm classes and generates ts definitions from them.

I haven't tried this yet, but it theoretically should work. Separate the API for your library (or an interface the api implements) into a kotlin common module. You can then compile the api into a jvm module, and run it through the ts-generator to generate ts definitions.

Maybe there is a clever way to do this to skip the compilation to jvm for ts definition generation.

In Kotlin 1.4-M1 support for exporting TypeScript definitions was added

Preview: TypeScript definitions

Another feature in the new Kotlin/JS IR compiler we’re excited to show off is the generation of TypeScript definitions from Kotlin code. These definitions can be used by JavaScript tools and IDEs when working on hybrid apps to provide autocompletion, support static analyzers, and make it easier to include Kotlin code in JS and TS projects.

For top-level declarations marked with @JsExport (see above) in a project configured to use produceExecutable(), a .d.ts file with the TypeScript definitions will be generated. For the snippet above, they look like this:

// [...]
namespace blogpost {
    class KotlinGreeter {
        constructor(who: string)
        greet(): string
    }
    function farewell(who: string): string
}
// [...]

In Kotlin 1.4-M1, these declarations can be found in build/js/packages/<package_name>/kotlin alongside the corresponding, un-webpacked JavaScript code. Please note that since this is only a preview, they are not added to the distributions folder by default for now. You can expect this behavior to change in the future.