Just a simple example of failed instanceof check when different filename letter cases are used in imports.
Repoduced on Mac OS.
So here we have error.js file that is imported in app.js and data.js
But in app.js it will be imported with lowercase letters and in data.js it will be imported with a capital letter.
In app.js we create instance of error from error.js and pass it to Data instance.
In Data instance we try to check instanceof but it will fail. BTW if you fix import (it should equal with app.js import) then instanceof check will pass.
Just run code with npm start and see in logs:
service check Error1 true
service check Error true
data check Error1 false
data check Error true