Error instance not preserved in `onRequestError` about next.js

[kevva]

@huozhi, I know you worked on the onRequestError feature. How would you advice handling cases like this where you need to know which kind of error that was thrown? Maybe I don't want to log all errors, maybe I have some other logic for some other errors.

const onRequestError = error => {
  if (error instanceof MyCustomError) {
    doSomeThingDifferent();
    return;
  }

  console.error(error);
};

If you want to keep error as a DigestError, the source error could be added to the context or something.

[huozhi]

If you're throwing an error in RSC layer, the error will be processed by react renderer and then being collected by the error reporter. So far we cannot get the actual instance or class of it as the thrown one could be anything and React needs to serialize it to a general error that can also be sent to client. From bundling perspective, the MyCustomerError is also bundled separately in the instrumentation entry and the page entry, they would beccome two separate classes. So instanceof might not work as expected here.

You could give it some other special property for example digest property that it will still be reused by react renderer and preserved during rendering serialization.