20 OOP in JavaScript Interview Questions and Answers

JavaScript is a programming language that is used to create interactive web pages. It is also used in server-side programming, game development and mobile app development. Object-oriented programming (OOP) is a programming paradigm that uses objects and classes to model real-world entities. OOP in JavaScript is used to improve the structure and organization of code. If you are applying for a position that involves JavaScript programming, you should be prepared to answer questions about OOP. In this article, we will discuss some common OOP questions that you may encounter during a job interview.

OOP in JavaScript Interview Questions and Answers

Here are 20 commonly asked OOP in JavaScript interview questions and answers to prepare you for your interview:

1. What is the difference between a class and an object in JavaScript?

A class is a template for creating objects. An object is an instance of a class. A class defines the properties and methods that an object will have.

2. Why are classes important in OOP? How do they help developers write better code?

Classes are important in OOP because they help to keep code organized and easy to understand. By creating classes, developers can more easily identify which code belongs to which object, and they can also more easily reuse code by creating new objects that inherit from existing classes. This helps to make code more maintainable and easier to work with over time.

3. Can you give me some examples of how to define a function within a class in JavaScript?

In JavaScript, functions are defined within a class by using the keyword “function” followed by the function name and parentheses. For example:

class MyClass {
function myFunction() {
// function body
}
}

4. Why can’t I use ‘this’ inside a static method in JavaScript?

The ‘this’ keyword in JavaScript refers to the object that is currently executing the code. In a static method, there is no object that is executing the code, so ‘this’ would have no meaning.

5. Can you explain what inheritance is?

Inheritance is a way for one object to inherit the properties and methods of another object. In JavaScript, this is typically done by using the prototype property.

6. Can you provide some examples of using inheritance in JavaScript?

Inheritance is a way to extend the functionality of an existing object by creating a new object that inherits the properties and methods of the existing object. In JavaScript, this can be done using the prototype property. For example, if you have a base object called “Person” that has properties and methods for a person’s name, age, and gender, you could create a new object called “Employee” that inherits from “Person” and also has properties and methods for an employee’s job title and salary.

7. Is it possible for a child class to call a parent class’s constructor in JavaScript? If yes, how?

Yes, it is possible for a child class to call a parent class’s constructor in JavaScript. This can be done using the super keyword.

8. What do you understand by polymorphism?

Polymorphism is the ability of an object to take on many different forms. In JavaScript, this means that a single object can be used to represent multiple different types of data. For example, a single object could be used to represent a person, a place, or a thing. This makes it easier to work with data that may have different properties, but which can be treated in a similar way.

9. Can you give me some examples of polymorphism in JavaScript?

In JavaScript, polymorphism refers to the ability of an object to take on multiple forms. For example, a function can be written in such a way that it can accept multiple data types as arguments. This is an example of polymorphism.

10. What is encapsulation?

Encapsulation is the process of hiding data and methods inside of an object, so that they can only be accessed by other code inside the object. This helps to keep the data and methods safe from being accidentally modified or accessed by outside code, which can help to prevent errors and bugs.

11. Can you explain how encapsulation helps improve code quality when programming in JavaScript?

Encapsulation is the process of hiding information inside of an object, and it is a key concept in object-oriented programming. By hiding information, we can prevent other parts of our code from accidentally changing data that they should not be changing. This helps to make our code more reliable and easier to debug.

12. What is data abstraction?

Data abstraction is the process of hiding the details of how data is stored and accessed from the outside world. In JavaScript, this can be accomplished by using objects and methods to encapsulate data. By doing this, you can prevent other code from directly accessing and manipulating your data, which can help to keep your code more organized and maintainable.

13. Can you explain how data abstraction makes working with JavaScript easier?

Data abstraction is the process of hiding data that is not relevant to the current task at hand. This can make working with JavaScript easier because it can help to reduce the amount of information that you need to keep track of at any given time. By hiding data that is not needed, you can focus on the task at hand and not be distracted by irrelevant information.

14. What are the two main aspects of object-oriented programming that you need to keep in mind while writing OOP scripts in any language?

The two main aspects of object-oriented programming that you need to keep in mind while writing OOP scripts in any language are encapsulation and inheritance. Encapsulation is the process of hiding data and methods inside of an object, while inheritance is the process of creating new objects that inherit the properties and methods of existing objects.

15. Can you give me some examples of objects in real life?

Some examples of objects in real life include:

-A car
-A house
-A person
-A book

16. What does “cloning” mean in the context of OOP?

Cloning in the context of OOP refers to the ability to create an object that is a copy of another object. This can be useful if you want to create a new object that has the same properties and values as an existing object, but you don’t want to modify the existing object.

17. How would you go about cloning an object in JavaScript?

There are a few different ways to clone an object in JavaScript. One way would be to use the Object.assign() method to create a new object and then populate it with the values from the original object. Another way would be to use the JSON.parse(JSON.stringify()) method to create a new object with the same values as the original object.

18. What is the difference between deep copy and shallow copy?

A shallow copy is a copy of an object that only copies the top-level fields, and any nested objects or arrays are references to the original object. A deep copy copies all fields of the object, and also makes copies of any nested objects or arrays.

19. Can you give me some examples of good use cases for implementing OOP in JavaScript?

There are many good use cases for implementing OOP in JavaScript. One example would be if you were creating a large application with many different components. Organizing your code into objects would make it much easier to manage and reuse code. Another example would be if you were creating a game. OOP would be a great way to organize your code so that you could easily create and reuse game objects like characters, enemies, and items.

20. Are there any downsides to using OOP in JavaScript? If yes, then which ones?

While there are many benefits to using OOP in JavaScript, there are also some potential downsides. One downside is that it can be easy to create objects that are tightly coupled, which can make code difficult to maintain and reuse. Another downside is that OOP can sometimes lead to code that is less efficient than other approaches, since objects typically require more memory than other data structures.