Table of contents

Introduction

ES6 Interview Questions for Freshers

2.1.

1. What is ES6?

2.2.

2. List some of the popular features of ES6?

2.3.

3. Why is Babel used?

2.4.

4. Briefly explain promises in ES6.

2.5.

5. Name the data types supported by JavaScript.

2.6.

6. What is an arrow function?

2.7.

7. Differentiate among let, const, and var.

2.8.

8. Which OOPs feature is supported in ES6?

2.9.

9. Differentiate between ES5 and ES6.

2.10.

10. Mention the three states of promises in ES6.

2.11.

11. What is meant by event propagation in ES6?

2.12.

12. Describe the working of callbacks in ES6.

2.13.

13. What is the purpose of the spread operator in ES6?

2.14.

JavaScript

2.15.

14. Write the code to import and export values in ES6.

2.16.

15. What is Exception Handling in ES6?

ES6 Interview Questions for Experienced

3.1.

16. Define the constructor in ES6.

3.2.

JavaScript

3.3.

17. What do you understand by destructuring in E6?

3.3.1.

Example:

3.4.

JavaScript

3.5.

18. How is inheritance achieved in ES6?

3.6.

19. List some string functions in ES6.

3.7.

20. What is meant by Set and WeakSet in ES6?

3.7.1.

Example:

3.8.

JavaScript

3.8.1.

Example:

3.9.

JavaScript

3.10.

21. What are template Literals In ES6?

3.10.1.

Example:

3.11.

JavaScript

3.12.

22. Briefly explain the Temporal Dead Zone.

3.13.

23. Explain the working of the Object.freeze(). How is it different from const?

3.14.

JavaScript

3.14.1.

Output:

3.15.

24. What do you understand by AJAX?

3.16.

25. Briefly explain the map in ES6.

3.16.1.

Example:

3.17.

JavaScript

3.18.

26. Define proxy in ES6.

3.19.

27. List the advantages of using arrow functions.

3.20.

28. Explain callback hell.

3.21.

29. Mention some advantages of using web pack.

3.22.

30. When should one not use arrow functions?

Conclusion

Last Updated: May 17, 2024

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ES6 Interview Questions

Author Akanksha Burnwal

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Introduction

Welcome Ninjas. Are you ready for your web development interviews? Are you looking for some of the most frequently asked ES6 questions and answers to ace your interviews? Here we are with the top 30 ES6 interview questions and answers that would help you enhance your ES6 knowledge and help clear your interviews.

Now, let us dive into some critical ES6 interview questions for freshers and experienced people interested in Web development.

ES6 Interview Questions for Freshers

The following section will increase your conceptual knowledge, strengthening your basics.

1. What is ES6?

After the standardization of JavaScript by the European Computers Manufacturers Association, it came to be known as ECMA Script. ES6 is the 6th edition of ECMA Script, released in 2016 with certain new features and concepts of arrays, promises, iterators, functions, and many more. The introduction of ES6 reduced the complexity of coding, thereby making front-end web development a lot easier.

2. List some of the popular features of ES6?

Ans: Some of the popular features of ES6 are:

ES6 supports immutable variables
The addition of arrow functions in ES6.
Block scope assistance for variables and functions
Enhanced OOPs properties
Promises
Template literals
Modules
Multiline Strings
Classes
Managing extended parameters
ES6 braces Map/Set along with WeakMap/WeakSet
Default parameters
Destructuring assignment

3. Why is Babel used?

Ans: Web Browsers do not understand ES5 and hence use a JavaScript transpiler, Babel, to convert modern JavaScript, also known as ES6, into browser-compatible ES5, which is embraced by all browsers.

Babel input (ES6):

[7, 8, 9].map(x => x+2);

Babel output (ES5):

[7, 8, 9].map(function(x) =>{
return x+2;
});

To install Babel, you must have NodeJs and npm installed in the system. Then you can type the command below in your VS terminal or Command prompt to install Babel.

npm i -save-dev babel-cli

4. Briefly explain promises in ES6.

Ans. JavaScript supports Asynchronous programming with the help of promises. While running the tasks independently from the main thread in asynchronous programming, promises are created which are either fulfilled or rejected based on an outcome. Before promises were introduced, callbacks were used to deal with asynchronous functions. But then, the anomaly of callback hell led to the introduction of promises in ES6.

5. Name the data types supported by JavaScript.

Ans. JavaScript supports seven data types:

Number
Boolean
String
undefined
null
Object
Symbol

6. What is an arrow function?

Ans: Arrow functions are a concise way of defining a function. The arrow function uses a fat arrow indicator.

function subs(a, b){
return a-b;
}
Using arrow function
const subs = (a, b) => a-b;

7. Differentiate among let, const, and var.

Ans:

let	const	var
A let variable has a block scope.	A const variable has a block scope.	A var variable has a functional scope.
The values of a let variable can be reassigned.	Const variable has restricted mutability.	The values of a var variable are mutable.
The let variable can be declared even without initialization.	Initialization of the const variable is necessary for a const variable.	Initialization is not required while declaring a var variable.

8. Which OOPs feature is supported in ES6?

Ans: ES6 comes with class-based OOPs property. It supports static methods, which instead of being bound to an instance of a class, actually belong to the class itself. ES6 also supports the inheritance property of Object-Oriented Programming by which a child class can inherit the properties of a parent class. The keywords super and extends used to implement inheritance.

9. Differentiate between ES5 and ES6.

Ans:

ES5	ES6
ES5 is the fifth version of ECMA Script, introduced in 2009.	ES6 is the sixth version of ECMA Script, introduced in 2015.
Variables can be declared only using the var keyword	Variables are declared using the let, const, and var keywords.
The data types supported by ES5 are Number, String, Boolean, null, void, and undefined.	Along with the data types of ES5, Symbol is another data type introduced in ES6.
Object manipulation uses more time in ES5	Object manipulation uses less time in ES5
In ES5, both the function keyword and return keyword are necessary to define a function.	In ES6, the feature of the arrow function does not require the function keyword to define the function.

10. Mention the three states of promises in ES6.

Ans: Promises in ES6 come with three states:

Pending: The initial state of a promise when it is neither fulfilled nor rejected is called the pending state.
Rejected: This states that the promised action was unsuccessful.
Resolved: This state marks the fulfillment of the promised operation and that it was a success.

11. What is meant by event propagation in ES6?

Ans: When an event is triggered on DOM, it does not totally happen on a single element. The event bubbles up to its parent and ancestor elements until it reaches the window in the bubbling phase. Next comes the capturing phase, where the event reverses its trajectory and progresses down, visiting every element until it gets the target element that prompted the event.

Thus event propagation can be divided into 3 phases, Capturing phase, the Target phase, and the bubbling phase.

12. Describe the working of callbacks in ES6.

Ans: Callback is a method or a function passed as an argument to another function. For the outside function to be executed, the function inside must finish its execution. It was used to run asynchronous programs in JavaScript.

13. What is the purpose of the spread operator in ES6?

Ans: Spread operator is used in ES6 to get a list of elements. It basically expands an array or an iterable into separate elements. It increases the readability of code.

For example,

JavaScript

JavaScript

let a=[..."mango"];
console.log(a);

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Output:

[‘m’, ‘a’, ‘n’, ‘g’, ‘o’]

14. Write the code to import and export values in ES6.

Ans: In ES6, we can import and export values using the code:

import module from “./module/module/module”
export module;

15. What is Exception Handling in ES6?

Ans: Exception Handling in ES6 is achieved by try and catch block. It is used to capture a block of code that may throw an error. Upon encountering an exception, the program ends in a very unpleasant manner. Thus exception handling comes into the picture.

Syntax:

try{
#code
[break;]
} catch (e) {  
   //code executed if there is an exception   
[break;]  
}[ finally {  
   //code that is executed even if an exception occurs 
}
]

ES6 Interview Questions for Experienced

16. Define the constructor in ES6.

Ans: A Constructor function is invoked every time an instance of a class is created. It has no return type. The properties of the object are defined by the user constructor which is further assigned with the parameter values passed to it.

JavaScript

JavaScript

class square {
  constructor() {
    this.side = 4;
  }
}
const sq = new square();
console.log(sq.side);

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Output:

17. What do you understand by destructuring in E6?

Ans: Destructuring refers to separating the values of an array into variables. Functions having multiple parameters are also used to implement destructuring.

Example:

JavaScript

JavaScript

let wish=['Happy', 'Birthday'];
let [w1, w2]=wish;
console.log(w1 + "+"+ w2);

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Output:

Happy+Birthday

18. How is inheritance achieved in ES6?

Ans: Inheritance is the oops property by which a child class acquires the characteristics of the parent class. The extends, and the super keyword is used to achieve inheritance in ES6. The extends keyword is used by the child class to inherit from the parent class, whereas to invoke the same parent class the super keyword is used .

19. List some string functions in ES6.

Ans:

String Function	Purpose
startswith	This string function returns true if a string starts with a particular prefix which is passed as an argument.
endswith	This string function returns true if a string ends with a particular suffix which is passed as an argument.
includes	The includes function checks if the string contains a given substring which is passed as an argument.
repeat	The function returns a new string that contains the number of copies passed as an argument.

20. What is meant by Set and WeakSet in ES6?

Ans: A Set is a collection of unique values. The values would be different in terms of the data type also.

Example:

JavaScript

JavaScript

const set_A = new Set (["a", "b", "c"]);
console.log(set_A.values());

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Output:

[Set Iterator ] {‘a’, ‘b’, ‘c’}

A WeakSet is a Set that contains only unique objects. Once an element here has no reference left or becomes inaccessible, it is transferred to the garbage collector and auto-destroyed.

Example:

JavaScript

JavaScript

function ninja() {
    const weak_set = new WeakSet();
	let ob = {
		Str1: "Hello",
		Str2: "World"
	}
	weak_set.add(ob);
	console.log("Weak_set has ob : " + weak_set.has(ob));
}
ninja();

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Output:

Weak_set has ob : true

21. What are template Literals In ES6?

Ans: One of the new features of ES6 is template literals. It generates multiline strings, thereby solving the issue of string concatenation. Template literals are also used to implement embedded expressions.

Example:

JavaScript

JavaScript

let str1='Hello';
let str2='World';
let str=`${str1} ${str2}`;
console.log(str);

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Output:

Hello World

22. Briefly explain the Temporal Dead Zone.

Ans: The let keyword is not used for variable hoisting in ES6. Thus the declarations do not increment at the topmost area of the execution context. ES6 gives a reference error whenever a variable is referenced without initializing it. Therefore the period between the variable binding and declaration in a program is known as the Temporal dead zone.

23. Explain the working of the Object.freeze(). How is it different from const?

Ans: Object.freeze() is used to create an object which is immutable, i.e., the values of the object cannot be changed.

JavaScript

JavaScript

let a={
x: 4,
}
let p=Object.freeze(a);
a.x=5;
console.log(a.x)

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Output:

4
 //Changes fail to be updated

On the other hand, the Const property is executed on variables such that they are immutable, i.e., one cannot change the value.

24. What do you understand by AJAX?

Ans: The full form of AJAX is Asynchronous JavaScript and XML. The collection of technologies, HTML, CSS, JavaScript, PHP, Python, Nodejs, etc., in AJAX can be used in such a way that without reloading, the web page data can be sent to the server and vice versa.

25. Briefly explain the map in ES6.

Ans: ES6 comes with the map data structure, a collection containing key-value pairs in which the values can be of any data type. Keys and values in the map can be either primitives or objects. The map can be used to create and implement hashmaps.

Example:

JavaScript

JavaScript

var map = new Map();
map.set(1, 'apple');
map.set(2, 'mango');
map.set(3, ‘banana’);
console.log(map.size);

You can also try this code with Online Javascript Compiler

Run Code

Output:

26. Define proxy in ES6.

Ans: Proxy refers to an API in ES6 that is used for metaprogramming in ES6. The proxy object defines the behavior of basic operations. The proxy object carries out specific actions in place of the real object.

27. List the advantages of using arrow functions.

Ans: The advantages of using the arrow function are:

Arrow functions considerably reduce the size of code.
The context inside the arrow functions in ES6 is defined lexically
Automatically binds this
Function or return keywords are not required.

28. Explain callback hell.

Ans: Callback hell comes into application while developing applications on the web. While writing thousands of lines of code, developers often find it tedious to manage the callback and hence use a nested callback to make their jobs easier. Multiple callback nesting is known as callback hell. Sometimes massive callback nesting can make your code messy and clog your application.

29. Mention some advantages of using web pack.

Ans: Web pack refers to a tool in ES6 that is used to compile javascript modules.

Some of the advantages of a web pack are:

The web pack comes with an included web server that makes development easier.
Using a web pack, developers can control how they deal with different assets.
Many modules and packs are grouped into a single .js file.

30. When should one not use arrow functions?

Arrow functions in JavaScript have a concise syntax and are commonly used to define anonymous or shorter, one-liner functions. However, there are situations where you should avoid using arrow functions:-

Constructor Functions: Arrow functions cannot be used as constructor functions to create instances of objects.
Event Handlers: When working with DOM event handlers, arrow functions may not be suitable, especially if you need to access event-specific properties.
Recursion: Arrow functions are not suitable for recursive functions because they are unable to reference themselves using a named identifier.
Methods in Objects: Arrow functions might not be the best choice when defining methods within objects because arrow functions do not bind their own "this" context but inherit it from the surrounding code.
Readability: You may prefer traditional functions with curly brackets and explicit return statements in applications with complex logic where readability is important.

The choice between arrow functions and traditional functions in JavaScript depends on specific requirements of your code, including context binding, readability and maintainability.

Conclusion

It is always better to have all the answers at your fingertips such that whenever a question is asked, you can answer them with a confident smile. Going through the above ES6 interview questions would help you resolve your doubts and ace your preparation for your interviews. It would help you clear your Web development interviews and work at your dream companies.

We wish the blog was insightful and that it benefited you in your preparations. Enhance your knowledge more by going through some of the related articles on Web Development.