feat(Grpc-Web): Add & export GrpcWebError type

[zakhenry]

This allows clients to declare the error type in an observable response, e.g.

const client = new DashStateClientImpl(rpc);
client.UserSettings({}).pipe(
  catchError((err: GrpcWebError) => {
    
    if (err.code === grpc.Code.FailedPrecondition) {
      // handle appropriately
    }
    
    return throwError(() => err)
    
  }),
);

[stephenh]

@zakhenry sorry for the late review here, this looks great!

Just curious, but wdyt about making this a class, like:

export class GrpcWebError extends Error {
  constructor(message: string, public code: grpc.Code, public metadata: grpc.Metadata) {
    super(message);
  }
}

As this would let callers do things like if error instanceof GrpcWebError.

[zakhenry]

yep I like it, commit pushed to implement this idea.

[stephenh]

@zakhenry what's the setPrototypeOf for? I've not seen it in constructors before.

[zakhenry]

@stephenh it is a recommendation for extending built-in classes to ensure instanceof checks still work. See https://github.com/Microsoft/TypeScript-wiki/blob/main/Breaking-Changes.md#extending-built-ins-like-error-array-and-map-may-no-longer-work where it first appeared.

I'm unsure if this is only an issue for certain compilation targets or not, however I do have a memory from the past where not having this line has caused problems

[zakhenry]

Reading around a bit I believe this is specifically for ES5 targets, see also https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error

[stephenh]

Ah huh! Okay... I guess one more naive question, but this makes it sound like the es2015 target doesn't have this issue:

https://www.dannyguo.com/blog/how-to-fix-instanceof-not-working-for-custom-errors-in-typescript/#upgrade-the-compilation-target

And given it's ~7 years after 2015 :-D do you think we could just drop this as probably not necessary anymore? Like is this specifically required for your app/target's target environment?

[zakhenry]

me personally nope, I'm targeting es2015 for my applications. I'll check what is the default support for things like create-react-app and the angular cli. If they support es5 out of the box as default I think grpc-web probably should too?

[zakhenry]

ok yep I create a fresh react app with typescript and tried it out and the instanceof check works fine. And Angular targets ES2017 by default. Happy to drop it

[zakhenry]

removed.

[stephenh]

Looks great, thanks @zakhenry !

[stephenh]

🎉 This PR is included in version 1.122.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release
• v1.122.0

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