OOP in JavaScript

This quiz covers key concepts of OOP in JavaScript to help you master its principles.

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Question 1

What is a class in JavaScript?

  • A built-in object for working with arrays

  • A blueprint for creating objects

  • A method for inheritance

  • A library for JavaScript functions

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Question 2

What is the purpose of the constructor method in a JavaScript class?

  • Initializes the class

  • Defines private methods

  • Creates a new instance of the class

  • Sets up properties for the class object

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Question 3

How do you create an instance of a class in JavaScript?

JavaScript 
class Person {
    constructor(name) {
        this.name = name;
    }
}


  • const p = new Person('Ajay');

  • const p = Person('Ajay');

  • const p = createInstance(Person, 'Ajay');

  • const p = Object.create(Person);

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Question 4

What does the extends keyword do in JavaScript?

  • Allows one class to inherit from another class

  • Creates a new instance of a class

  • Binds a method to a class

  • Defines static methods in a class

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Question 5

What is encapsulation in JavaScript OOP?

  • Using a constructor to initialize properties

  • Inheriting properties from a parent class

  • Combining multiple classes into one

  • Restricting direct access to object properties and methods

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Question 6

What will the following code log?

JavaScript 
class Animal {
    makeSound() {
        console.log("Generic sound");
    }
}
class Dog extends Animal {
    makeSound() {
        console.log("Bark");
    }
}
const pet = new Dog();
pet.makeSound();


  • Generic sound

  • Bark

  • Error

  • Undefined

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Question 7

What is polymorphism in OOP?

  • A way to define private properties

  • Combining classes into a single object

  • Using the same method name but with different implementations in child classes

  • Sharing methods between unrelated objects

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Question 8

What are static methods in JavaScript classes?

  • Methods only accessible to instances of the class

  • Methods accessible only on the class itself

  • Methods that are inherited by subclasses

  • Methods that override the constructor

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Question 9

What will the following code log?

JavaScript 
class Vehicle {
    static start() {
        console.log("Starting vehicle...");
    }
}
Vehicle.start();


  • Starting vehicle...

  • Error

  • Undefined

  • Starting

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Question 10

Which of the following best describes inheritance in JavaScript?

  • Creating a new class from a string

  • Sharing properties and methods between objects of the same type

  • Deriving a new class from an existing class to reuse code

  • Encapsulating object properties

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There are 10 questions to complete.

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