Update error masking example in the docs

[borekb]

formatError expects the returned error to be of type GraphQLFormattedError and the example was using return new Error(...) which caused TypeScript error.

The updated code just rewrites the message without changing the rest of the object.

[abernix]

Out of curiosity, have you verified that making the change in this way (as in, modifying the existing error) doesn't change the representation of the error which is used in non-response avenues? Specifically, the error received by apollo-engine-reporting's rewriteError [#2618] method, and the error received by the didEncounterError life-cycle hook [#2719])?

[borekb]

I didn't – I have actually never used rewriteError or didEncounterError.

Sorry if this PR isn't valid but just copy/pasting the example to our code threw errors.

[abernix]

Related to #1884, perhaps? @borekb, I'm curious if that solution does the trick for you?

import { ApolloError } from 'apollo-server-errors';
throw new ApolloError('Error!');

(Just want to point out that it's unfortunate that this is the way that formatError works and that a more clean solution hasn't been implemented earlier, but we'll get there!)

[borekb]

@abernix I'm not sure I understand – do you mean I should throw an error instead of returning it?

---

To sum up (all inside formatError), this what the docs say:

if (err.message.startsWith("Database Error: ")) {
  return new Error('Internal server error');
}

This is what works for me:

if (err.message.startsWith("Database Error: ")) {
  err.message = 'Internal server error';
}

Is this what you're proposing?

if (err.message.startsWith("Database Error: ")) {
  throw new ApolloError('Internal server error');
}

[abernix]

Superseded by #2966. Hope that works for you! We'll get it into a release soon.