DNG - Client Extension Examples with Typescript + React
One answer
If you look at the RM Client API link it tells you how to find this:
The JavaScript API for RM comes with a typescript interface definition file that facilitates the development of extensions in typescript. The interface definition file is included in the server installation. You can download the file from a running server by using a URL; for example:
https://example.com:port/rm/web/com/ibm/rdm/web/extensions/api/interface/RM_API.d.ts