parent.active is true, and child was created with parent as its prototype. What does "active" in child evaluate to?
undefined, because inherited properties have no boolean result
false, because only child's own properties are searched
true, because the inherited property is found✓Правильный ответ
A TypeError, because in cannot inspect prototypes
Объяснение
The in operator searches both the object and its prototype chain, so the inherited active property makes the test true. Saying false because child lacks an own property mistakes this operator for an ownership-only check.