JavaScript Prototypes and Classes 2

Question 1

What does `Object.getPrototypeOf(obj)` return?

Accepted Answer

The prototype of obj

Answer

`Object.getPrototypeOf(obj)` returns the prototype (i.e., the value of the internal `[[Prototype]]`) of the specified object.

Question 2

Which keyword is used to call the parent class constructor inside a subclass?

Accepted Answer

super()

Answer

`super()` must be called in a subclass constructor before using `this`, invoking the parent class constructor.

Question 3

What is the result of `typeof class Foo {}`?

Accepted Answer

'function'

Answer

Classes in JavaScript are syntactic sugar over functions, so `typeof` returns `'function'`.

Question 4

How do you define a static method in a JavaScript class?

Accepted Answer

Using the `static` keyword before the method

Answer

The `static` keyword defines a method that belongs to the class itself, not to instances.

Question 5

What happens when you access a property that doesn't exist on an object or its prototype chain?

Accepted Answer

It returns undefined

Answer

JavaScript traverses the prototype chain and returns `undefined` if the property isn't found anywhere in the chain.

JavaScript Practice Test