Top 25+ ES6 interview questions and answers

Top 25+ ES6 interview questions and answers
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Here is the best es6 programming interview questions and answers for freshers and experienced professionals to crack the interview fast.


ES6 is the script name given to the JavaScript language. It is the sixth update to the JavaScript. ES6 is also known as ECMAScript 6 and ECMAScript 5. JavaScript is a name given to the language for marketing purpose. For standardization of language and its specifications, it was given to a body for standardization for information and communication for technology, which is European Computer Manufacturer Association (ECMA). So it was named ECMAScript in the beginning after eventual language standardization.

First edition of the language was announced in June, 1997. ES6 was announced in June, 2015. It was announced as EcmaScript6 (ES6), which was later renamed to ECMAScript 2015.

Interview questions on ES6

Q: What is ES6?

A: It is a standardized language for JavaScript. ES6 is sixth language update for JavaScript (JS).

Q. What are some new features of ES6?

A: Following are some new features of ES6:

  • Support for constants
  • Block-Scope support for constants, functions
  • Extended Parameter Handling
  • Destructuring Assignment
  • Exciting new features: Modules, Classes, Iterators, Generators
  • New Enhanced Object Properties
  • Now Support for Map/Set & WeakMap/WeakSet
  • New Enhanced Regular Expression
  • Promises
  • Meta-Programming,Internationalization and Localization
  • Template Literals and Extended Literals
  • Arrow functions

Q: What is let keyword?

A: Let is an option which lets you declare a variable with black scope.

Q: What is const keyword?

A: The const statement let you declare a const. In const, value cannot be changed. They must be given value at the time of declaration. Contants are immutable variables.

Q: What is arrow function? How to create it?

A: Arrow function is a concise syntax alternative for writing functions expression in ES6. Arrow function is also called ‘fat arrow function’ for, it uses => fat arrow marker.

Q: What are advantages of arrow functions?

A: Following are advantages of Arrow Functions:

  1. Arrow functions are very succinct and less verbose than normal functions.
  2. Arrow functions have lexical binding, which makes your code very easy and comfortable. Arrow functions take the ‘this’ argument from surroundings, and you do not require bind () or const that = this anymore.

Q: How to download ES6?

A: Follow these commands:

  1. Installation of Rollup
  2. File Structure
    1. Create two files: src and dest. Also create Index.html .
  3. Create a Configuration File, and name it rollup.config.js
  4. Load the script file in HTML
  5. Setup Js files.
  6. Compile ES6 into ES5

Q: What is Modules ES6 ?

A: ES6 Module Transpiler is a powerful tool which compiles your ES6 into ES5 compatible code in Common JavaScript or ADM style.

Q: How to export and import Modules?

A: You can export and import modules using following commands:

  • import Module from ‘./Module/Module;
  • export Module;

Q: Explain Destructuring Assignment in ES6?

A: Destructuring assignment is a new feature in ES6. It is very advantageous. It helps developers to extract data from array and objects into separate variables.

let full_name =[‘Paul’,’Ferrara’];

let [first_name,last_name]=full_name;


// outputs Paul Ferrara

Another example

let c=[400,700,660,900];

let [a,…b]=c;


// outputs 400 [700, 660, 900]

Q: What is Webpack?

A: Webpack is an open source JavaScript module bundler which creates an environment that supports and runs Babel.

Q: What are template literals in Es6?

A: Template Literals are defined as string literals, which allow embedded expressions. Template literals in ES6 are very beneficial and better than normal literals built with quotes. Template literals allow you to work with strings in a better way compared to ES5. They allow concentration and interpolation in much more unique and clear manner.

Let’s see an example of concentrating a string in JavaScript (JS):

var a=”Hey”;

var b=”Paul”;

var c = a+ ” ” + b;

Console.log(c); //outputs Hey Paul;

You can do concentration and interpolation by back tick “ in a single line. In order to interpolate a variable, put in to {} braces forwarded by $ sign.>/p>

// In ES6

let a=”Hey”;

let b=”Paul”;

let c=`${a} ${b}`;

console.log(c); //outputs Hey Paul;

Q: Explain Constants in Es6?

A: In ES6, a constant is declared by a const keyword. ES6 provides a const keyword, which a constant uses and declares a const.

Q: What is Babel?

A: Babel is a JS Transpiler, which allow us to write in ES6 and translate the work done in ES6 into ES5 which is supported by browsers.

Q: List steps to install Babel?

A: Follow these steps:

Requirements for installation process of Babel:

  1. Node.Js
  2. Npm

You must have Node.Js installed on your server. To check, if Node.Js is installed, use these commands:

node -v

npm -v

Installation of Babel: Now, you can install Babel CLI by running following command in terminal:

npm install –save-dev babel-cli

Q: List benefits of using Webpack?

A: Following are benefits of using Webpack:

  1. Multiple modules and packs are bundled into a single .js file.
  2. It has integrated dev server. You only need to include one JS tag pointed to server like localhost:8080/assets/bundle.js , and get live code updating and asset management in no costs.

Q: How to create a Javascript class in ES6?

A: You can create a class in JavaScript using following command:

Class User{

constructor(name,age) { = name;

this.age = age;


getData() {

console.log( + ” is ” + this.age + ” years old !”);



var user = new User(“foo”, 7);


Q: What is Spread Operator in ES6?

A: By using spread operator, you can manipulate arrays and objects in new way. Spread Operator, which is represented as “…” spreads the variable. For example:

function print(…z){




Q: How to debug in ES6?

A: Follow these steps:

  1. Installation of Node.js 8.x
  2. Configure a New ES6 Project
    • Start by creating a new nmp project and launch it in VS code:
      • $ mkdir debug-es6 && cd debug-es6 $ npm init -f $ code
    • Instal Babel Module:
      • $ npm install –save-dev babel-cli babel-preset-es2015
    • Update Package.json
      • “devDependencies”: { “babel-cli”: “^6.24.1”, “babel-preset-es2015”: “^6.24.1” }, “babel”: { “presets”: [ “es2015” ] }
    • Create a src file and src/math.js
      • xport function add(num1, num2) {

return num1 + num2;

}export function multiply(num1, num2) {

return num1 * num2;


    • Create  src/app.js to
      • import {add, multiply} from ‘./math’;const num1 = 5, num2 = 10;console.log(‘Add: ‘, add(num1, num2));
      • console.log(‘Multiply: ‘, multiply(num1, num2));
  • Configure Babel to Transpile ES6 to ES5
  • Add launch configuration
    • Debug -> Open Configurations” and choose “Node.js”
  • Debug your application

Q: Will ES6 Support Backend?

A: yes, ES6 will support Backend.

Q: What are Promises in ES6 ?

A: In order to support asynchronous programming, promises deliver a clearer way to implement async programming in JavaScript (ES6 new feature).

Q: What is Set?

A: Set: Set is a collection of unique values, in which duplicate values are ignored. All values must be unique. Values can be object references or primitive types.

Q: What is map?

Map: Map can be defined as elements that are stored as keys, or value pairs. Objects or primitive values can be stored in map as either key or value.

Q: What is Weakmap?

Weakmap: In WeakMap, keys are objects, and they can be of any arbitrary value.

Q: What is Weakset?

Weakset: Weakset helps you in storing weakly holding objects in a collection. An object occurs only once, for it is unique in the weakset collection.

Q: What is difference between ES6 and typescript?

A: There is no exclusive difference between ES6 and Typescript. You can perform functions in ES6 which you can perform in Typescript. Only difference is that transcript can create ECMAScript only.

Q: What is difference between CoffeeScript and es6 ?

A: Difference between CofeeScript and ES6:

Difference between CoffeeScript and ES6 is that CoffeeScript has all new features that ES6 has, and it compiles into JavaScript. But ES6 is a next level language, which uses compiler like Babel to convert code into ES5 (current version of JavaScript).

Q: what is meant by Class Expressions?

A: Class Expressions mean to define a class in ES6. Class expression are named and unnamed, both. It uses prototype-based inheritance.

Q: What is Generator function?

A: It is a new exciting feature of ES6, in which values can be generated over time by returning an object which iterates to pull values from the function one value at a time.

Q: What is default parameters?

A: Default parameters are parameters which permit named parameters to start with default values if no value or undefined passes.

Q: What is Generator function?

A: generator is a function which behaves like an iterator. It can stop, and resume from where it stopped earlier.

Q: How can you filter an array of objects in ES6?

A: You can filter array of objects in ES6 by following commands:

var testArray = [{“name”:”Sheeba”, “age”: 26},

{“name”:”Nida”, “age”: 22},

{“name”:”Naheed”, “age”: 5 },

{“name”:”Naila”, “age”: 20 }];

var data = testArray.filter(person => person.age > 18); //Filters the Array of Objects to condition set



0:{name: “Sheeba”, age: 26}

1:{name: “Nida”, age: 22}

2:{name: “Naila”, age: 20}




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