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Advanced JavaScript Interview Questions And Answers

Advanced JavaScript Interview Questions And Answers

Whenever the coder starts to build any website or any web applications that time the JavaScript plays a very major important role with them. As we all know the JavaScript is designed to add interactivity to HTML pages. If you people are attached to a web developer career or if you are looking for a career in this then you should clear with the basic JavaScript concept and you should know the JavaScript questions and its answer that could ask you at the time of interview. You should clear a few details before applying the position of Web application developer about JavaScript, as the JavaScript is used to validate data at user end systems, it is used to create cookies such as help to retrieve information users system and JavaScript is used at client-side scripting language, it also reacts as events.

The JavaScript is an object-oriented language, and very lightweight, used to cross-platform translated language. It is a client-side scripting language. You could translate JavaScript code into a web browser. This language has less server interaction and the user's feedback is very quick. It is a very popular language for building server-side software. In this article, we will discuss object-oriented JavaScript interview questions and answers.

Please tell me about JavaScript?

Sample Answer – According to my knowledge, it’s the very important scripting language and commonly used at server-side scripting, and interpreted programming language. It is also an object-oriented language that helps to create interactively into Html pages. And it is embedded with web browsers; it is open-source platform language as well.

Please tell us what are the different data types in JavaScript?

Sample Answer – In JavaScript, the data type areas, a) Object b) String c) Boolean d)String e)Symbol f)Null g)Undefined

Tell us the difference between java and JavaScript?

Sample Answer - I would like to tell you, Java is a programming language while JavaScript is a scripting language. Java helps to create applications that could be run in a virtual machine or any browser while in JavaScript the code is run on the browser only. Java code gets compiled before program runs while JavaScript codes are all in the form of text.

Please tell me the syntax, how can you create an object in JavaScript?

Sample Answer - First I would like to tell you the JavaScript helps Object-oriented concepts, where we can create the object as follows, And the need for the creation of variable in his syntax as,

var Stu = {

name: “Joy”,

age: 23


How to create an Array in JavaScript, and what is the syntax?

Sample Answer - We could define array in JavaScript as follows, var a = []; var b =[1, 2, 3, 4, 5 ];     

Tell us the variable naming convention in JavaScript, what it is?

Sample Answer - First thing we cannot use JavaScript reserved keywords as variable names.

In JavaScript the variable name should not start with any numbers; it must begin with a character or underscore character. In JavaScript, the variables are case sensitive. JavaScript variables are case sensitive.

For an example,

var  anyname;   -> correct

var  9_name;       ->incorrect

var  _5_name;     -> correct

Can we assign an anonymous function to a variable, and what is your view in this?

Sample Answer - In the anonymous function, we can easy to assign an anonymous function to any named variable and we can pass it as an argument to any other function.

Tell us the scope of the variable in JavaScript?             

Sample Answer - The scope variables in JavaScript are a) Global variable – its type of global variable could be declared outside the function in the program of JavaScript. b) Local variable - The variable declaration is done inside the function.

Tell us about callback in JavaScript?                

Sample Answer - It is one type of function in JavaScript language that passes a method as an argument. The functions are executed step by step so that it is called a callback function.

What is the syntax of using cookies and how you could create a cookie using JavaScript?

Sample Answer – First I would like to tell you, we could save any document by writing a document dot cookie file.  And after that we can assign a string value to the cookie;

Cookies Syntax: - doc. cookie =”cookiename=value_01; expires = day,date,time";

What is closure in JavaScript, please tell?

Sample Answer - When our variable is defined outside the scope that time we create closures. It helps for accessing outside the function scope in our inner function of the program. To use a closure, define a function within another function and representation it.

What are the advantages of JavaScript, please tell?

Sample Answer - According to me, there are many are the advantages of JavaScript language –

  • This language has very little server interaction here we can validate user input data before sending the page off to the server. So, that data traffic can manage and the load page becomes on the server getting less.
  • Here we can get the user's immediate feedback so that it could save their time of reloading.
  • We could use the interface the components of drag and drop, and slider in JavaScript to include an interface to your user side.

Tell us the different ways to define a variable in JavaScript?

Sample Answer - There are the ways to define a variable in JavaScript are as follows: a) Var b) Const c) Let.

Var - With the help of this, we can give a value to the variable. And its declaration is done before execution.

Let – Here the variable can be reassigned by this keyword.

Const – Here, we cannot change the value of constant it is a fixed variable. When a function is declared as const, it can be called by any type of object.

Tell us about the “TypeOf” operator, what it is?

Sample Answer - It is one type of operator which is used to get the data type of the operand. And the operand can either be any data structure. In JavaScript, the variable, function, object, is a unary operator that can place before a single operand.

How you read a cookie using JavaScript?

Sample Answer - We can put the value as string in the cookie and the name as the like cookie. The syntax and use of cookies as below - doc. cookie string will have a list of name = (Need to write the value pairs by use of semicolons), there more one thing we can use the split () function to break the string into key and value as well.

Tell us the difference between Attributes and Property?

Sample Answer - The Attributes always provide the details on an element like id, type, value, etc. And the property is the value that can be assigned to the property like id=” “, value=’Name’ etc.

Tell us the different ways the HTML element can be accessed in a javascript code?

Sample Answer - There are different ways to access html element into JavaScript code with help of mentioned property -

a) getElementById(‘idname’)

b) getElementsByClass(‘classname’)

c) getElementsByTagName(‘tagname’) d) querySelector().

Tell us the type of JavaScript Frameworks?

Sample Answer - Mostly following frameworks are used in  JavaScript a) Angular b)React c) Vue

Tell us different JavaScript code can be involved in an HTML file?

Sample Answer - There are different types of JavaScript code involved in an HTML file. In the Inline JavaScript, the function that can create at runtime is assigned to a variable. We can differentiate between inline and anonymous functions. An inline function is assigned to a variable and can be easily reusable as well. Also, we could use the Internal and external javascript when we need for the function or we can either have the integrated script on the page or we can place it in a separate file that we need to call when it requires

Tell us about a Typed language?

Sample Answer - The language in which values are associated with values and not with the variables. First is dynamical - variable can accept multiple types of data like number, chars.

Second is statically - here the variable cannot accept multiple types of data; like a string in java can accept only characters.

Please tell us the difference between Local storage and Session storage in JavaScript?

Sample Answer - Following is the difference between local storage and session storage as,

In general, I would like to tell you, the local server basically uses to minimize the traffic in between client and server systems and we can clear its local storage through manually via the setting option, because here data is never sent back to the server from the request of the HTTP server. The session storage does not have a specific time duration, because its data gets cleared when our page session request end or when we close our system browser.

What is the setTimeout() function in javascript, please tell?

Sample Answer - It has a very important role like when this method is used at that time all functions have to wait till time finishes.

Tell us the difference between null & undefined?

Sample Answer - The Undefined is a kind of variable which we can declare but its values never assigned it, and we can say that it is one type of self type. The Null represents no value and Null is the object value and we can assign it to any variable with the representation of no value.

What is the difference between undeclared and undefined, please tell me about it?

Sample Answer - In JavaScript, the undeclared variables do not exist in a program and are not declared. Undefined variables are declared in the program but have not given any value.

What is the innerHTML & innerText, please tell about?

Sample Answer – It’s basically the both are vice versa such as

a) innerHTML – The innerHTML will process an HTML tag is found in a string.

B) innerText – It is opposite to innerHTML as the innerText will not process an HTML tag is found in a string.

Write the syntax of Call & Apply, what it is?

Sample Answer - There are the syntax that can use to write a call and apply function,

Syntax of call :[, arg1 [, arg2 [, arg3 [, ---]]]]), and the

Syntax of Apply : fun.apply(thisArg,   [argsArray]).

Which method reverses the elements of the array, name it?

Sample Answer - The reverse method reverses the elements of the array. The first element gets last and last elements to get the first in this method. Syntax method - array.reverse();

How you can add a new element in the array?

Sample Answer - We can use push function to add one or more elements in the array it can return a required added value.

Kindly tell, which method sorts the elements of the array?

Sample Answer - It is very simple the sort method can sort the elements of the array.

Tell us about the prototypal Inheritance?

Sample Answer- in JavaScript, the Prototype is a rule, with the help of a prototype we can create a new object and when the object will create after it then it will inherit the properties of the main parent object.


From this article, we concluded that all these JavaScript and advanced JavaScript interview questions of 2020 will help you to understand the basics of JavaScript as well as to prepare for advanced JavaScript interviews. You could also go through the pdf of JavaScript interview questions for better help. 

You may read more, and get details on How to Hire a Great JavaScript Developer which would be helpful to you.


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