JavaScript Prototypes and Classes 3

Question 1

What does the `hasOwnProperty()` method check?

Accepted Answer

Whether a property exists directly on the object (not inherited)

Answer

`hasOwnProperty()` returns `true` only if the property belongs directly to the object, not inherited via the prototype chain.

Question 2

What is the value of `Animal.prototype.constructor` after `class Animal {}`?

Accepted Answer

Animal

Answer

By default, `prototype.constructor` points back to the class (or function) itself.

Question 3

Private class fields in JavaScript are declared with which prefix?

Accepted Answer

#

Answer

The `#` prefix declares a truly private field that is only accessible within the class body.

Question 4

What does `class B extends A {}` set as `B.prototype`'s prototype?

Accepted Answer

A.prototype

Answer

When extending a class, `B.prototype` is given `A.prototype` as its prototype, establishing the inheritance chain.

Question 5

Which of the following correctly overrides a parent method in a subclass?

Accepted Answer

Define a method with the same name in the subclass

Answer

Defining a method with the same name in the subclass shadows the parent's version due to prototype chain lookup order.

JavaScript Practice Test