JavaScript Prototypes and Classes 4

Question 1

What is the prototype of a regular function's prototype object (e.g., `function Foo(){}`)?

Accepted Answer

Object.prototype

Answer

By default, a function's `.prototype` object inherits from `Object.prototype`, just like any regular object.

Question 2

What is the purpose of `Object.setPrototypeOf(obj, proto)`?

Accepted Answer

Set the prototype of obj to proto at runtime

Answer

`Object.setPrototypeOf()` changes the `[[Prototype]]` of an existing object, though it is discouraged for performance reasons.

Question 3

Which accessor type allows you to run logic when a class property is read?

Accepted Answer

getter

Answer

A `get` accessor (getter) runs a function when the property is accessed and returns its return value.

Question 4

What does `instanceof` check?

Accepted Answer

Whether an object's prototype chain includes the constructor's prototype

Answer

`instanceof` checks if `Constructor.prototype` exists anywhere in the object's prototype chain.

Question 5

What happens if you call a class constructor without the `new` keyword?

Accepted Answer

It throws a TypeError

Answer

Classes enforce being called with `new`; calling them without it throws a `TypeError: Class constructor cannot be invoked without 'new'`.

JavaScript Practice Test