JavaScript Interview Questions - NullClass

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JavaScript Interview Questions

JavaScript Interview Questions


Top 50 JavaScript Interview Questions and Answers for 2021 | Edureka



In this blog you will be provided with a list of the top interview questions for JavaScript! If you are preparing for coding interview in JavaScript. You will also be provide with a list of the frequently asked questions.

1) What is JavaScript?


What is JavaScript? | JavaScript Programming | Edureka


  • JavaScript is a scripting language. It is very different from the Java language. It is an object-based, lightweight, cross-platform translated language. It is a very widely used language for client-side validation. With the help of the translator used in JavaScript (embedded in the browser) we can translate the JavaScript code for the web browser.

2) List a bunch of features of JavaScript.

A few of the features of JavaScript are:

  • JavaScript it a Lightweight scripting language,
  • It is an Interpreted programming language,
  • It is good for the applications which are network-centric in nature,
  • It is Complementary to the java programming language.
  • It is also complementary to hyper text markup language or HTML,
  • It is an Open source scripting language.
  • Along with all these amazing features another one of its mind boggling feature is that it is a cross-platform scripting language.

3) Who developed JavaScript, and what was the initial name of JavaScript?


What is JavaScript used for? | Hack Reactor

  • Brendan Eich was the developer of JavaScript, who was a Netscape based programmer. Brendan Eich developed this new amazing scripting language in just a course of ten days in the year September 1995. At the time of its launch, JavaScript was called Mocha. But, after that, it was called Live Script and later known as JavaScript (which is its current name).

4) List a few of the amazing advantages provided to us by JavaScript.

Some of the advantages of JavaScript are:

  • Interaction with server is very less.
  • Feedback to the visitors is almost immediate.
  • Interactivity is extremely high
  • Interfaces are way richer as compared to other scripting languages.

5) List some of the disadvantages that JavaScript has.

Some of the disadvantages in JavaScript are:

  • No support is provided for multithreading.
  • No support is provide for multiprocessing.
  • Reading and writing of files is prohibited.
  • No support is provided for networking applications.

6) Define a named function in JavaScript scripting language.


A quick introduction to JavaScript


The function which has named at the time of definition is called a named function. For instance:

  1. function msg()
  2. {
  3.   document.writeln(“Named Function”);
  4. }
  5. msg();

7) Name the types of functions provided by JavaScript.

The types of function in JavaScript are:

  • Named function- This type of function contains name at the time of the process of definition. For instance:
    1. function display()
    2. {
    3.   document.writeln(“Named Function”);
    4. }
    5. display();
  • Anonymous function- This type of function doesn’t contain any name. They are declared dynamically during the runtime.
    1. var display=function()
    2. {
    3.   document.writeln(“Anonymous Function”);
    4. }
    5. display();

8) Define the anonymous function

  • It is a type of function that has no name (as is suggested by its title xD). This type of function is declared dynamically at runtime using the function operator () instead of the function declaration. The function operator is way more flexible than a function declaration. It can easily be used in the place of an expression. For instance:
  1. var display=function()
  2. {
  3.   alert(“Anonymous Function is invoked”);
  4. }
  5. display();

9) Can a variable be assigned an anonymous function?

Yes, you can certainly assign an anonymous function to a variable.

10) In JavaScript what is the argument object?

The variables of JavaScript represent the arguments that are passed to its function.

11) Define the term closure in context with JavaScript.


Closure in JavaScript through examples - jomendez


  • In the case of JavaScript, we need closures while a variable which is defined outside the scope in reference is accessed from an inner scope.
  1. var num = 10;
  2. function sum()
  3. {
  4. document.writeln(num+num);
  5. }
  6. sum();

12) If we wish to return the character from a specific index which method gets used?

  • The JavaScript string charAt() method is used in order to find out a char value present at the index that is specified. The index number starts from 0 and goes to n-1, wherein n is the length of the string. The index value can never be a negative integer, greater than or equal to the length of the string. For instance:
  1. var str=”Javatpoint”;
  2. document.writeln(str.charAt(4));

13) What is the main difference between JavaScript and JScript?

  • Netscape which is provided the JavaScript language. Microsoft has changed the name and called it JScript to avoid the trademark issue. In other words, you can say JScript is exact the same as JavaScript, but Microsoft provides it to us.

14) How to write hello world instance of JavaScript?

  • A very simple instance of JavaScript hello world is under mentioned. You need to place it inside the body tag of HTML.
  1. <script type=”text/javascript”>
  2. document.write(“JavaScript Hello World!”);
  3. </script>

A list of a bunch of more questions you can prepare for your JavaScript interview are:

15) What are the key differences between Java and JavaScript? / How is JavaScript different from Java?

16) How to use external JavaScript file?

17) Is JavaScript case sensitive language?

18) What is BOM?

19) What is DOM? What is the use of document object?

20) What is the use of window object?

21) What is the use of history object?

22) How to write a comment in JavaScript?

23) How to create a function in JavaScript?

24) What are the different data types present in JavaScript?

25) What is the difference between == and ===?


  • Thank you very much for reading this blog! If you come up with any doubts or queries then do not hesitate to contact us! I hope I was able to brief you on the top interview questions for javascript or Jscript! I hope you have a wonderful rest of your day! And I want to wish you all the very best for your interview. Have a bright, bright future ahead 🙂

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1. What is Java?

  •      Java is the high-level, object-oriented, robust, secure programming language, platform-independent, high performance, Multithreaded, and portable programming language.

2. Features of Java Programming language? 


  • Object-Oriented
  • Simple
  • Portable
  • Secured
  • High performance
  • Multithread

3. What do you understand by Java virtual machine?

  • Java Virtual Machine is a virtual machine that enables the computer to run the Java program. JVM acts like a run-time engine which calls the main method present in the Java code.

4. What is the platform? 

  • A platform is the hardware or software environment in which a piece of software is executed. There are two types of platforms, software-based and hardware-based. Java provides the software-based platform.

5. What are the main differences between the Java platform and other platforms?

  • Java is the software-based platform whereas other platforms may be the hardware platforms or software-based platforms.
  • Java is executed on the top of other hardware platforms whereas other platforms can only have the hardware components .




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