[Illniyar]

I'm not following, why can't I use:

   e instanceof Error

or:

   e instanceof MyError

why does toString() have anything to do with this?

[prodigal_erik]

It's very likely someone did

  const e = new Error('bad stuff happened')
  e.name = 'MyError'

without actually creating a MyError class to check with instanceof.

[Illniyar]

Unless it's common in popular libraries/packages, I don't see why I need to take it into account.

Which popular libraries do this?

If it's just in a few places, it should be handled specifically, and use sane choices in other places.

[pags]

This is what I do when working with my own Error types.