JavaScript Classes Interview Questions

1. What are classes in JavaScript?

Classes in JavaScript are used to encapsulate code and data to work ahead. They are special functions that also need declaration and expressions.

2. What is the difference between a function and a class declaration?

The most striking difference between function declarations and class declarations is hoisting. Function declarations are always hoisted whereas class declarations are not.

3. What is the difference between classical and prototypal methods of inheritance?

Classical inheritance is a powerful feature of an object-oriented programming language.

Under this, methods from the base class are inherited into the derived class. Here, objects are considered an abstraction of real-world entities. The concept of classical inheritance implements a greater level of generalization.

Prototypal Inheritance is when functions are inherited directly from other objects. It does not work as increasing layers of abstraction.

In classical inheritance, new methods cannot be added at runtime since classes are immutable.

Since prototypes are flexible and either mutable or immutable, the above problem is rarely encountered.

Classical inheritance is complex and might not necessarily support multiple inheritances.

Prototypal Inheritance is simple and supports multiple inheritances.

4. What are transpiling classes? Name one.

Classes that act as translators in a particular necessity are called transpiling classes. They render a code originally written in ECMAScript 2015 to be translated into JavaScript so that any browser can understand. The new code can run in any environment. The most popular among developers is Babel.

5. Is it necessary to create a constructor?

Constructors are methods that are written to initialize instance variables of the class. It is not necessary to create one, since in the absence of a coded constructor, a default constructor. It is an empty function that does not modify the instances.

6. What is encapsulation?

Encapsulation is the process of binding variables and functions acting on data. This allows us to validate and control the data. Keyword var is used to encapsulate data.

7. What is the super keyword?

The keyword super refers to the parent class. It helps to access the parent class while in the child class.

8. How is the keyword extends useful?

Besides creating an instance of a class, JavaScript allows you to create sub-classes. The keyword extends is used in class expressions or declarations of the derived or sub-class.

9. What is the error boundary in class?

A class component in JavaScript can become an error boundary component when it defines a static getDerivedStateFromError() or componentDidCatch(error, info).

10. What do you mean by WeakMap?

The WeakMap object is a collection of many key/value pairs in which all such keys are weakly referenced. The keys in the collection must consist of objects and the values could be all sorts of arbitrary values.

11. Why are getters and setters used in a JavaScript program?

The prime function of getters and setters is to define the object accessors.
The benefits of the getters and setters in a code.
It makes the syntax simple.
It equalizes syntax for properties and methods alike.
These can secure a better quality of data.
It proves useful for doing things in the backdrop.

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