Top 17 Interview Questions for a JavaScript Developer


May 16, 24

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7 minutes





    Table of content
  • First and foremost, determine your job requirements
  • What should be done to prepare for a JavaScript interview?
  • Relinns Careers Website
  • The following are the top 17 JavaScript interview questions and answers
  • Conclusion
Relinns Careers Website

You are well aware that your JavaScript project's success depends on your ability to locate top javascript developers, whether you are an entrepreneur, a project manager in a major organization, or a C.T.O.

 This guide contains sample interview questions and answers that you may use when looking for a new JavaScript developer to bring your dynamic user interfaces to life. You'll also get some pointers on using these questions to find the top candidates for the job reliably.

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First and foremost, determine your job requirements

The most common mistake interviewers make is not knowing what type of JavaScript developer they seek before sitting down with their applicants. And, no, "an awesome JavaScript developer with much experience" is not detailed enough.

 It would help if you located the proper candidates capable of consistently accomplishing your project's JavaScript-specific duties with your team. To accomplish so, you must first determine your specific employment requirements.

 Some examples of JavaScript developer requirements include:

  • HTML and CSS are essential to web development skills.
  • JavaScript-specific abilities include libraries and toolkits, as well as testing code.
  • Design abilities – creating scalable programs, as well as security
  • Communication abilities – Discussing issues and constraints
  • Self-initiative entails figuring out solutions on one's own

Make a list of non-essential talents for your ideal JavaScript developer instead. Instead, concentrate on what your candidate will be doing daily. Keep your list of needs as short as feasible. Remove anything that they can live without or learn on the job.

You'll be able to choose the correct JavaScript developer job interview questions and better understand what kinds of responses you're looking for if you have clearly stated requirements.

What should be done to prepare for a JavaScript interview?

Preparing for a JavaScript developer job interview entails conducting a study on less familiar issues in a solution-oriented manner. Furthermore, the following points can assist you in succeeding:

  • Understanding J.S. concepts like callbacks, hoisting, promises, and I.I.F.E. before interview-based coding activities, as well as its genesis and future scope in the programming business
  • Demonstrating your mastery of current J.S. features by developing two code solutions to a problem
  • While this list is limitless, aspiring Javascript developers should additionally research and implement the company's standard coding practices during the interview.

The following are the top 17 JavaScript interview questions and answers

Here are some questions you should consider for your preparation:

1. What exactly is the distinction between JavaScript and JScript?

This question assesses your fundamental knowledge of the programming language.

"Both languages are similar, except that Jscript is Microsoft's version of JavaScript," for example. 

2. How can you determine the operating system of a client's device with Javascript? 

It demonstrates your ability to collaborate with clients while also testing the fundamentals of your client-server expertise as a JavaScript developer.

"The navigator.userAgent or navigator.appVersion properties help identify the client's O.S.," for example.

3. What contribution does the Push function provide to JavaScript?

This question examines your in-depth understanding of changing the number of elements in an array. Concentrate on regulating array ecosystems.

"By utilizing numerous arguments, it is possible to append one or more components to the end of the array." The Push method can also be used to change the length of an array."

4. How do a confirmation box and an alert box differ? 

Javascript developer job interviewers ask this question to determine how well you can write code that simplifies the message for the user.

"Both of these boxes convey a message to the user." While the alert box only has one clickable option (OK), the confirmation box has two (OK and CANCEL)."

5. What are the two methods for reading and writing files in J.S.?

This Javascript developer job interview question assesses your basic usability with the programming language.

"A file can be read/written in Javascript via a web page and Active X objects, or J.S. extensions," for example.

6. Exactly what are global variables?

It assesses the javascript developer's knowledge of decreasing the use of local variables and saving memory.

"A global variable is when the var keyword, used to declare a localized object or variable, is missing." Furthermore, global variables are used throughout the code to eliminate any constraints."

7. Identify the three J.S. looping structures 

Loops are a common component in any programming language and demonstrate the coders condense more extended codes into shorter ones.

"For, While, and Do-while are the three looping structures" is the answer Javascript developers can give.

8. In J.S., what is the result of 5+9+ "2"? 

This quiz checks your understanding of how numerical calculations are performed in J.S. programming.

"As two is placed within a string, it will be concatenated to the sum of 5+9," for example. As a result, the output is 142."

9. What is the definition of D.O.M. in J.S.? 

D.O.M. aids in the management of web content using code. The coder gains access to a web page's components using D.O.M. in J.S.

"Document Object Model is built automatically by the web browser once the page has loaded." The D.O.M. allows access to modification of any element of the webpage."

10. What are the functions of window.onload and onDocumentReady?

Both of these functionalities are associated with loading the web page and code; explain your replies in terms of which functionality manipulates the code more quickly.

"While onDocumentReady downloads the code just before the D.O.M. is available, it allows the coder to change the code early." Window.onload, on the other hand, does not begin until all webpage information is ready. Furthermore, it causes delays before the code is executed." 

11. What is the difference between a break and a continued statement? 

Both of these terms are related to the looping part of programming. Explain how the break and to continue statements affect loops.

"Whereas the break statement forces an exit from a running loop, the continue statement allows the same loop to continue running with a new start." 

12. What are the three categories of failures that J.S. flags? 

These errors are generated automatically and classified into three types. You'll make a strong impression if you can demonstrate your code-resolving ability and a broad understanding of how these issues occur.

"In J.S., there are three categories of faults: load-time, runtime, and logic errors." Any of these flaws will disrupt the program's smooth operation."

13. Identify the two primary classes of data types in J.S.

It explains your adaptability when utilizing a wide range and amount of factors.

"Primitive and Reference data types are the two core kinds of data types in J.S." Primitive types only represent numbers and Booleans. In contrast, reference types include more complicated data types like strings and dates." 

14. What is the distinction between attributes and properties? 

Attributes- give additional information about an element such as id, type, value, etc.

Property- is the value allocated to the property, such as type="text", value='Name", and so on.

15. How do you define a variable in JavaScript?

In JavaScript, there are three ways to describe a variable:

Var- The JavaScript variables statement declares a variable and, optionally, initializes its value. Variable declarations are handled before code execution, for example, var a =10.

Const- The principle behind const functions is that they should not affect the object they are called. When a part is declared const, it can be reached on anything.

Let – It indicates that the variable may be reassigned, such as a counter in a loop in an algorithm. It suggests that the variable will be utilized in the block in which it is defined. 

16. What exactly is a typed language? 

Values in Typed Language are associated with values rather than variables. There are two kinds of it:

Dynamically: The variable can store various types; for example, a variable can take a number or a string.

Statically: The variable can only retain one type, such as in Java, where a variable specified as a string can only hold a collection of characters and nothing else. 

17. What is the distinction between local and session storage?

Local Storage: Data is not sent back to the server for each HTTP request (HTML, pictures, JavaScript, CSS, and so on), decreasing traffic between client and server. It will remain until manually cleared via settings or an application.

Session Storage: Similar to local storage, the only difference is that data stored in session storage is erased when the page session ends. Still, data kept in local storage has no expiration period. 

If you have any troubles with these JavaScript Interview Questions, please leave a comment below.


Hiring the proper personnel for your development team is essential to the project's success. Remember that your goal should not be to employ the best JavaScript developer but rather the best individual for the job.

With the help of this knowledge and sample JavaScript developer job interview questions, you can ensure that the recruiting process goes quickly and successfully, allowing you to hire a fantastic programming team to execute your project on time.

We hope reading this article was helpful to you! 


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