Vend a typeguard function for checking if an Error is a PurchasesError

[bilalq]

Hey. When using TypeScript, the type of the caught error is unknown (any in non-strict mode of older versions of TypeScript). It would be very useful to have a typeguard function vended that could narrow the type. Would you be willing to accept a PR that implements this?

export const isPurchasesError = (err: unknown): err is PurchasesError => {
  // Implementation here
}

The usage would look like:

try {
  await someCodeThatTriggersAPurchase()
} catch (err) {
  if (isPurchasesError(err)) {
    // Handle PurchasesError here. 
    // The type will be narrowed by the compiler and IDE completion will work nicely.
  } else {
    // Handle other errors differently
  }
}

This is something we can of course just write on our own end, but it seems like it'd be useful to have as part of the core library here.

[bilalq]

I don't see this being controversial, so I think I'll go ahead and just make the change and submit a PR soon.

[aboedo]

I just realized that we forgot to reply here!!! I'm sorry about that @bilalq 🤦

This is a great idea! Thanks for opening up the ticket.

We're more than happy to review the PR 🙌

[taquitos]

@bilalq did you happen to make any progress with this? We're going through all our issues now to make sure we keep things fresh 😄

[djw27]

Does this do the job?

import { PurchasesError } from 'react-native-purchases';

const isRevenueCatPurchaseError = (error: any): error is PurchasesError => {
  return error.domain === 'RevenueCat.ErrorCode';
};