JavaScript Prototypes and Classes 5

Question 1

What does `Object.create(null)` produce?

Accepted Answer

An object with no prototype at all

Answer

`Object.create(null)` creates a truly empty object with no `[[Prototype]]`, so it doesn't inherit from `Object.prototype`.

Question 2

In a class, what is the difference between a getter defined inside and a property assigned in the constructor?

Accepted Answer

Getters go on the prototype; constructor assignments go on the instance

Answer

Getters/setters defined in a class body are placed on `ClassName.prototype`, while properties assigned via `this.x = ...` in the constructor are own properties of each instance.

Question 3

What is 'prototype pollution' in JavaScript?

Accepted Answer

Maliciously modifying Object.prototype to affect all objects

Answer

Prototype pollution is a vulnerability where an attacker modifies `Object.prototype`, causing all objects to inherit malicious properties.

Question 4

What is the output of `console.log([] instanceof Array)` in JavaScript?

Accepted Answer

true

Answer

`Array.prototype` is in the prototype chain of any array literal, so `instanceof Array` returns `true`.

Question 5

How can you call a parent class static method from a subclass static method?

Accepted Answer

super.methodName()

Answer

Inside a subclass static method, `super.methodName()` correctly calls the parent class's static method.

JavaScript Practice Test

JavaScript Practice Test

JavaScript Prototypes and Classes 5