System.register __moduleName support

[guybedford]

I don't mean to be making work, but I think it's worth generically supporting this __moduleName identifier for System.register at this point and it is a relatively simple addition to the format of the form:

System.register([], function(_export, __moduleName) {
  // ...
});

This allows use cases like relative dynamic loading relative to the module being executed. The argument can even be omitted when it is not needed with binding detection as well.

Up until now I've been avoiding this hoping to make the second argument to System.register the ES loader module context which will provide similar functionality, but I don't think this contextual spec will be appearing for quite some time yet and the use case needs to be properly supported in the mean time.

For the original issue see systemjs/builder#416, and just let me know if there are any questions at all.

[capaj]

👍

[DanielRosenwasser]

@guybedford is this something that TypeScript users are supposed to use directly? I'm not familiar with the intended usage here.

[guybedford]

Yes this is a user API, for use cases like for relative dynamic loading:

export function loadNewStuff() {
  return System.import('./parent-relative', __moduleName)
  .then(function(stuff) {
    // ...
  });
}

[DanielRosenwasser]

Spoke offline with @vladima about this and this seems reasonable, but to support this automatically, we'd have to specially support a hard-coded __moduleName in the type system, which we'd need to discuss.

The more-likely workaround is that that users would need to define an uninitialized var-scoped variable named __moduleName like so:

declare var __moduleName: string;

Given that, I'm going to say we should wait on @mhegazy to return to make that call.

[guybedford]

Thanks for the feedback. A user-level declaration like that sounds fine to me.