An example of how to configure your TypeScript setup such that you can step into sub modules when debugging
git clone https://github.com/CodeOfLight/typescript-module-debub-v1.git
cd typescript-module-debub-v1
npm --prefix ./helpers install
npm --prefix ./app install
cd app
npm run via_ts-node
code .
Now add a breakpoint on line 3 of index.ts
var result = mathTools.addOne(4)
Press F5 to have VS Code start debugging
You should be able to step into the addOne() function which is defined in the @testlibs/helpers module and you should step into the TypeScript code and not the JS code.