Advanced JavaScript Interview Questions

Last updated on Feb 07, 2024
  • Share
Advanced JavaScript Interview Questions

Over the years, JavaScript has become one of the most influential programming languages in the software industry. Due to this, there are a number of job applications and applicants in this industry. Due to this, we decided to come up with the actual Advanced JavaScript Interview Questions, questions that actually matter while you create codes for your company. Have a read on these questions to cement your knowledge in JavaScript and get that dream job. But, over time, we have found out that many developers lack a basic understanding of JavaScript such as working on objects and working on obsolete patterns like deeply layered inheritance hierarchies.

What's in it for me?

We have created this section for your convenience from where you can navigate to all the sections of the article. All you need to just click or tap on the desired topic or the section, and it will land you there.

JavaScript Coding Interview Questions

Here in this article, we will be listing frequently asked Advanced JavaScript Interview Questions and Answers with the belief that they will be helpful for you to gain higher marks. Also, to let you know that this article has been written under the guidance of industry professionals and covered all the current competencies.

Q31. What is Temporal Dead Zone in ES6?

In ES6, Temporal Dead Zone is a behavior occurring in JavaScript while declaring a variable with the let and const keywords. The period between entering the scope and being declared is the one when these keywords cannot be accessed and enter the Temporal Dead Zone.

For example

console.log(foo); // undefined
var foo = 123;

console.log(foo); // Error
let foo = 123;

Also Read: JQuery Questions

If you consider that the const and let are also in place, why can't they be accessible before they are declared? The answer is within the idea of the Temporal Dead Zone.

Variables declared with let and const are stored and placed in the Temporal Dead Zone. Therefore, they cannot be accessible before the declaration is executed during the step-by-step process of scripting.

Temporal Dead Zone is the duration that let and const declarations are not accessible. Declarations of the let as well as const declarations are not accessible.

Temporal Dead Zone is activated when code execution is entered into the block that includes let or const declarations. It continues until the lets or const declaration. It continues until the declaration is executed.

Q32. Is JavaScript as Pass by value or pass by reference language?

Interestingly enough, it is both. Primitive types like number, string, etc. are passed by value, but objects can be passed-by-value (when we consider a variable holding an object is a reference to the object) and also as a pass-by-reference (when we consider variable to the object is holding the object itself).

Q33. How to "deep-freeze" an object in JavaScript?

To ensure that an object is deep-frozen, you will have to create a recursive function for freezing each property of type object: Without deep freeze.


let person = {
    name: "Ankit",
    profession: {
        name: "content writer"
Object.freeze(person); = "content writer";

Output { name: 'Ankit', profession: { name: 'content writer' } }

Now, using Deep Freeze for the object,

function deepFreeze(object) {
    let propNames = Object.getOwnPropertyNames(object);
    for (let name of propNames) {
        let value = object[name];
        object[name] = value && typeof value === "object" ?
            deepFreeze(value) : value;
    return Object.freeze(object);
let person = {
    name: "Ankit",
    profession: {
        name: "content writer"
deepFreeze(person); = "content writer";

Q34. Why is the "this" operator inconsistent In JavaScript?

In JavaScript, this operator always refers to the object, which is invoking the function being executed. So, if the function is currently being used as an event handler, this operator will refer to the node which fired the event.

Q35. How to calculate the Fibonacci series in JavaScript?

Here's the code to calculate the Fibonacci series in JS code:


var the_fibonacci_series = function (n)
  if (n===1)
    return [0, 1];
    var a = the_fibonacci_series(n - 1);
    a.push(a[a.length - 1] + a[a.length - 2]);
    return a;


Q36. What is JavaScript Hoisting?

A JavaScript default behavior that moves the declaration of variables and functions at the top of the current scope is called JavaScript hosting. You can use hosting for declaration, not for initialization.


Hoisting in JavaScript is a method where a function or variable may be utilized prior to declaration.

1. Variable hoisting

console.log(x); // undefined
var x = 1;

2. Function hoisting

let x = 20, y = 10;
let result = add(x,y);
function add(a, b) {
     return a + b;

Q37. What is the difference between arrow functions & normal functions?

1) Using the arrow function, you can get the same results as normal functions by writing a few lines of code as shown in the example below.

//Example of Regular function:
var add = function(c, d) { return c + d;};

// Example of Arrow function
let add = (c, d) => { return c + d}; //or
let add = (c, d) => c + d;

2) In normal functions, argument binding is possible and other hand arrow functions have no argument binding.

3) Regular functions are construable but arrow functions are not constructible.

Q38. How to remove duplicate values in an array with JavaScript?

There are two methods to remove duplicate content from an array such as using a temporary array and a separate index.

1. Using indexOf() Method

const getUnique = (arr) => {     
    let uniqueArr = [];    
     for(let i of arr) {
        if(uniqueArr.indexOf(i) === -1) {
const array = [1, 2, 3, 2, 3,4,5];


[ 1, 2, 3, 4, 5 ]

2. Using Set Method

let chars = ['A', 'B', 'A', 'C', 'B'];
let uniqueChars = [ Set(chars)];


[ 'A', 'B', 'C' ]

Top 10 Advanced JavaScript Interview Questions

Here you will find the list of Top Advanced JavaScript Interview Questions, which were written under the supervision of industry experts. These are the most common questions and usually asked in every interview for the role of the JavaScript Developers.

  • What is prototype?
  • What is Callback hell?
  • What is callback?
  • What are the difference between arrow functions & normal functions?
  • What is JavaScript Hoisting?
  • What are the difference between let, var & const?
  • What is Promises?
  • What is the difference between Map & filter function?
  • How to remove duplicate values in array?
  • What are Closure?
  • What is rest & spread operators?
  • What are the data types used in JavaScript?
Reviewed and verified by Umesh Singh
Umesh Singh

My name is Umesh Singh having 11+ experience in Node.JS, React JS, Angular JS, Next JS, PHP, Laravel, WordPress, MySQL, Oracle, JavaScript, HTML and CSS etc. I have worked on around 30+ projects. I lo...