SystemJS: Listing all registered functions

Is there a way in SystemJS to list all registered functions?

I want to find all TypeScript classes, which are transpiled to functions. But with SystemJS's System.register(...), these are not put to global object, but somewhere into SystemJS's internals.

Can I reach this list of registered functions / classes / modules / whatever? I didn't find anything such in the docs here.

If that's not possible for any reason (the modern frameworks tend to keep things trapped in closures), what would be the approach to get to such list? I only need subclasses of certain class (speaking about TypeScript), so I was thinking about catching the moment when the class gets extended. Or maybe some SystemJS callback, or rewriting System.register()?