Javascript Oops Interview Questions
Common Interview Questions About JavaScript Object-Oriented Programming
JavaScript is a popular object-oriented programming language used for creating dynamic and interactive web applications. During an OOP interview, candidates are often asked about the principles and concepts of OOP, such as encapsulation, inheritance, and polymorphism. They may also be asked to provide examples of how these principles are implemented in JavaScript, as well as explain the difference between class-based and prototype-based inheritance in the language. Other common questions may include how to create and use objects, constructors, and methods in JavaScript, as well as how to handle error handling and object manipulation. A strong understanding of OOP principles and their application in JavaScript is essential for creating efficient and maintainable code.
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1 - What is object oriented programming?
Object oriented programming (OOP) is a programming paradigm that focuses on creating objects that contain both data and procedures to manipulate that data. It allows for the organization and management of complex code by breaking it down into smaller, reusable objects.
2) What are the four principles of OOP?
The four principles of OOP are abstraction, encapsulation, inheritance, and polymorphism. Abstraction refers to the concept of hiding the internal implementation details of an object and only exposing relevant information. Encapsulation is the process of binding data and functions together within an object to protect its data from being directly accessed. Inheritance allows new classes to be based on existing classes, inheriting their attributes and behaviors. Polymorphism refers to the ability of objects to take on multiple forms, depending on their context.
3) What is a class?
A class is a blueprint or template for creating objects. It defines the properties and behaviors that all objects of that class will have. A class can also be seen as a user defined data type.
4) What is an instance?
An instance is an object that is created based on a class. It has its own set of data and can access the properties and methods defined in its class.
5) What is the difference between a class and an object?
A class is a template or blueprint for creating objects, whereas an object is an instance of a class with its own set of data and behavior.
6) What is data encapsulation?
Data encapsulation is a fundamental concept of OOP that refers to the process of hiding the internal details of an object's implementation. It allows for data to be accessed only through defined methods, ensuring that the data is protected and not directly manipulated.
7) What is a constructor?
A constructor is a special method that is used to initialize objects of a class. It typically has the same name as the class and is automatically called when an object is created.
8) What is the purpose of inheritance?
Inheritance allows for the creation of new classes based on existing ones. It promotes code reuse, reduces redundancy, and allows for the creation of hierarchical relationships between classes.
9) What is method overriding?
Method overriding is a feature of OOP that allows a subclass to provide its own implementation of a method defined in its superclass, instead of using the implementation provided by the superclass.
10) What is method overloading?
Method overloading is the ability to have multiple methods with the same name, but different parameters or arguments. This allows for the creation of multiple methods with different behaviors based on the type or number of parameters passed in.
11) What is polymorphism?
Polymorphism is the ability of an object to take on different forms. In OOP, this refers to the fact that objects can have different behaviors depending on their type or the context in which they are being used.
12) What is the difference between composition and inheritance?
Composition is a design pattern where an object contains one or more instances of other objects, thereby forming a part whole relationship. Inheritance, on the other hand, is a relationship between two classes where one class, called the subclass, inherits properties, and methods from another class, called the superclass.
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13) How does OOP promote code reusability?
OOP promotes code reusability through features such as inheritance and polymorphism. By allowing new classes to be based on existing ones, it reduces the amount of code that needs to be written from scratch and promotes the reuse of code.
14) What is a static method?
A static method is a method that can be called directly on a class without the need for an instance of that class. It is commonly used for utility or helper functions, and only has access to static variables and other static methods.
15) What is the importance of interfaces in OOP?
An interface is a collection of abstract methods that provide a contract for classes to implement. It allows for the creation of loosely coupled code and promotes a cleaner design by separating the definition of functionality from its implementation.
16) What is the difference between a private and a protected access modifier?
When a class member is declared as private, it can only be accessed within the same class. Protected members, on the other hand, can also be accessed from subclasses or classes within the same package.
17) What is the difference between an abstract class and an interface?
An abstract class can contain both abstract and non abstract methods, whereas an interface can only contain abstract methods. A class can only extend one abstract class, but can implement multiple interfaces.
18) What is the purpose of the “this” keyword?
The “this” keyword refers to the current object instance and is used to access its properties and methods within the class. It can also be used to differentiate between instance variables and local variables with the same name.
19) What is a package?
A package is a way of organizing and categorizing related classes and interfaces. It also helps in preventing naming conflicts and allows for access control through access modifiers.
20) What is the difference between a shallow copy and a deep copy?
A shallow copy creates a new object with the same values as the original object, but it still references the same object with the same reference. A deep copy creates a new object with the values of the original object, but it also creates new references for all the objects referenced by the original object. This ensures that the copied and original objects are completely independent of each other.
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