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Top 50 JavaScript Interview Questions You Must Prepare in 2020

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Nowadays, Google and Facebook help JavaScript to create complex, desktop-like web applications which are user-friendly. JavaScript has also become one of the most popular languages for structuring specific server-side software. Nowadays, even the internet isn’t large enough to keep up with JavaScript’s versatility. Professionals believe that programmers are already aware of these live facts and have come up with a solution.

JavaScript Online certifications

Getting JavaScript Online certifications after passing the JavaScript interviews is not the easiest, and many individuals spend numerous hours and days pounding through disintegrated coding questions to develop confidence. While lots of practice makes all the difference, but it also matters how you do your practice. Having a well-designed plan will help you master all the basic and advanced knowledge and JavaScript Interview Questions that interviewers expect from candidates.

So, if you are planning to start your career in JavaScript and you wish to advance your skills related to it, this is the right time to opt for it when the technology is in its advancing state. These JavaScript Interview Questions will offer you wholesome knowledge of programming and help you prepare for your JavaScript interviews:

JavaScript Interview Questions

  • What is the difference between Java & JavaScript?
  • What is JavaScript?
  • Which data types are supported by JavaScript?
  • What are the features of JavaScript?
  • Is JavaScript a case-sensitive language?
  • What are the advantages of JavaScript?
  • How can you develop an object in JavaScript?
  • How can you build an Array in JavaScript?
  • What is a name function in JavaScript, and define it?
  • How will you assign an anonymous function to a variable and pass it as an argument to another anonymous function?
  • What are the various argument objects in JavaScript, and what will you do to get these types of arguments passed to a function?
  • Mention the different scopes of a variable in JavaScript.
  • Mention the purpose of the ‘This’ operator in JavaScript?
  • What is Callback?
  • What is Closure? Give an example.
  • What are the different built-in methods and the values returned by them?
  • How does TypeOf Operator work?
  • How to create a cookie using JavaScript?
  • How to read a cookie using JavaScript?
  • How to delete a cookie using JavaScript?
  • Mention the different ways in which an HTML element can be executed in a JavaScript code.
  • What are the different ways a JavaScript code can be included in an HTML file?
  • Mention the different ways to define a variable in JavaScript.
  • What is a Typed language?
  • Point out the difference between Local storage & Session storage.
  • List the difference between the operators ‘==‘ & ‘===‘?
  • What is the difference between undeclared & undefined?
  • Name some of the JavaScript Frameworks
  • Mention the difference between window & document in JavaScript.
  • Mention the difference between innerHTML & innerText.
  • What is an event bubbling in JavaScript?
  • What is NaN in JavaScript?
  • How do JavaScript primitive/object types pass in functions?
  • How will you convert the string of any base to an integer?
  • What would be the result of 2+5+”3″?
  • What are Exports & Imports?
  • Mention the purpose of ‘Strict’ mode in JavaScript?
  • What is a prompt box in JavaScript?
  • How will you enable the ‘Strict’ mode in JavaScript?
  • What is the difference between Call & Apply?
  • How to empty an array in JavaScript?

Give the output of the following code:

//nfe (named function expression)

var Foo = Function Bar()


return 7;


typeof Bar();

  1. Give the output of the following code.

var Employee =


company: ‘xyz’


var Emp1 = Object.create(employee);

delete Emp1.company Console.log(emp1.company);

  1. Give the output of the following code.

var X = { Foo : 1};

var Output = (function()


delete X.foo;

return X.foo;




  1. Give the output of the code below.

var Output = (function(x)


Delete X;

return X;




  1. Why will you cover the entire content of a JavaScript information file in a function book?
  2. What are escape characters in JavaScript?


Individuals wanting to learn JavaScript and build their applications, then check out various online Full Stack Web Developer Masters Program which comes with trainer-led live training and lives project experience. JavaScript training will make you develop your skills to work with back-end and front-end web technologies. It also involves training on Web Development, Angular, MongoDB, jQuery, NodeJS, and ExpressJS.

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