Extending Boom and unexpected instanceof behavior

[wallacethefmh]

Support plan

• is this issue currently blocking your project? no
• is this issue affecting a production system? no

Context

• node version: v14.17.1
• module version: 9.1.2
• environment (e.g. node, browser, native): node
• used with (e.g. hapi application, another framework, standalone, ...): hapi
• any other relevant information:

How can we help?

https://github.com/hapijs/boom/blob/80528a674af77703cb8d0be15b50a655225d5cae/lib/index.js#L92

Doesn't this code break the expected behavior of class hierarchy/polymorphism?

const Boom = require('@hapi/boom').Boom; undefined class A extends Boom{}; undefined class B extends A{}; undefined const a = new A(); undefined a instanceof B; true

I see that removing that part of the Boom class doesn't fix the problem, since the Boom constructor actually returns a decorated Error and not an instance of itself. It's a bit strange.

It took me a while to figure out why instanceof for a subclass wasn't behaving like all other javascript classes, maybe it would just be worth adding something to the docs explaining the implications of extending Boom?

[kanongil]

Interesting. So the problem is that sub-classes inherit the Symbol.hasInstance method? I would not have guessed that.