JavaScript Objects and Classes Quiz

1. What is the purpose of the spread operator (...) in object literals?

Delete object properties

Copy and merge object properties

Create nested objects

Freeze object properties

2. Which approach best demonstrates encapsulation in JavaScript classes?

Making all properties public

Using private fields and public methods

Avoiding methods entirely

Using global variables

3. What is the purpose of the 'new' keyword when creating an object?

Delete the previous object

Create a new instance and call the constructor

Clone an existing object

Declare a variable

4. In class syntax, what does a static method belong to?

The class itself, not instances

Every instance of the class

The global object

The prototype only

5. What does the instanceof operator check?

If a variable is null

If an object is an instance of a class

If two objects are equal

If a property exists

6. Which method checks if a property exists directly on an object (not inherited)?

Obj.hasOwnProperty(prop)

Obj.hasProperty(prop)

Obj.includes(prop)

Obj.contains(prop)

7. What is polymorphism in the context of JavaScript classes?

Having multiple objects of the same class

Methods with same name but different behavior in subclasses

Creating objects without a class

Preventing inheritance

8. How do you prevent an object from being modified in JavaScript?

Object.seal()

Object.freeze()

Object.lock()

Object.protect()

9. What does Object.keys() return?

An array of object property names

An array of property values

A list of methods only

The prototype chain

10. In JavaScript, what is the difference between == and === when comparing objects?

No difference; both compare value and type

== compares values; === compares references

Both always return false for objects

Only === exists; == is deprecated

11. What is the primary purpose of a constructor function in JavaScript?

Initialize object properties and set up initial state

Delete objects from memory

Define global variables

Create prototype chains only

12. How do you copy all enumerable properties from one object to another?

Object.assign(target, source)

Object.copy(target, source)

Object.clone(target, source)

Object.merge(target, source)

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

An object with no prototype

An empty array

A null value

An object with Object.prototype

14. Which method allows you to define a property with a getter and setter?

Object.defineProperty()

Object.create()

Object.assign()

Object.freeze()

15. What is the correct way to define a private field in a modern ES2022 class?

#fieldName

_fieldName

Private fieldName

@fieldName

16. In a subclass, which keyword calls the parent class constructor?

Parent()

Super()

Base()

Inherit()

17. How do you create a subclass that inherits from a parent class in ES6?

Class Child extends Parent {}

Class Child inherits Parent {}

Class Child : Parent {}

Class Child < Parent {}

18. What does the 'this' keyword refer to inside a class method?

The global window object

The current instance of the class

The parent class

The function scope only

19. Which statement correctly demonstrates object property access using bracket notation?

Obj.propertyName = value

Obj[propertyName] = value

Obj->propertyName = value

Obj::propertyName = value

20. In ES6 class syntax, what keyword is used to define a method that runs when an object is created?

Init

Create

Constructor

Setup

JavaScript Institute Objects and Classes Quiz