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  • Karl Giesing thinks this is interesting:

a general behavior from a parent class can be overridden in a child class to give it more specifics.

From

Cover of You Don't Know JS: this & Object Prototypes

Note

That's not the idea that (subtype) polymorphism describes. Polymorphism means that a subtype may be treated as a parent type by users of that type.

The child class might override the behavior of the parent class, but it also might not, and it won't matter to the type's users.