GObject.type_is_a

function type_is_a(type: GObject.Type, is_a_type: GObject.Type): Boolean {
    // Gjs wrapper for g_type_is_a()
}

If is_a_type is a derivable type, check whether type is a descendant of is_a_type. If is_a_type is an interface, check whether type conforms to it.

type: type to check anchestry for
is_a_type: possible anchestor of type or interface that type could conform to
Returns: true if type is a is_a_type