JavaScript Developer Interview Questions

Top 10 JavaScript Developer Interview Questions

Securing great developers is a key component to the success of your software development project. These top JavaScript developer interview questions can lend you a hand in your recruitment efforts. 

Software development is a very technical field. As such, you need job candidates with the right skills and knowledge about the latest tools and technologies. 

To achieve this, you need to ask fundamental interview questions that reveal your applicants’ technical and soft skills. 

Top JavaScript Developer Interview Questions

When interviewing JavaScript developers, you need to ask questions that test their skills and knowledge. These questions will allow you to do that. Plus, you can better evaluate if these potential new hires have the attitude that best fits your company culture. 

1. Can you briefly explain what JavaScript is?

This is a question that tests a candidate’s foundational knowledge about JS. No matter the JS developer’s level, they should be able to explain JavaScript in their own words.

Sample answer:

To put it simply, JavaScript is an object-based, weakly and dynamically-typed, and interpreted programming language. It is considered one of the three core technologies alongside CSS and HTML in the software development world. JS is a client-side language, although it is now also used for back-end development. 

2. What is the difference between undeclared and undefined variables?

This one is another fundamental question for JS developers. Regardless of work experience, these developers should be familiar with both terms. Knowing the difference between the two is important to help troubleshoot scripting errors.

Sample answer:

Undeclared variables don’t exist as they were not declared anywhere in the program. A runtime error would occur when a JavaScript program tries to read an undeclared variable.

On the other hand, undefined variables are variables that are declared yet don’t have assigned values. There will be no error when a JavaScript program tries to read an undefined variable; it simply returns the variable. 

3. What is a JavaScript callback function?

You can ask this question to test a candidate’s basic JavaScript skills. Candidates should be able to answer this question quickly if they have the JS basics down. And to further test their knowledge, you can also ask them to provide an example.

Sample answer:

As its name suggests, a callback function is a function that is called after another function was executed. The function is then called back after completing an operation after being passed to another function as an argument. 

4. There are constantly new developments in JavaScript. How do you keep up with the latest JS libraries?

All great developers have the drive to learn and improve constantly. With questions like this, you can learn how passionate the candidate is about keeping up to date in his or her field of expertise.

It would help if you took note of their answers. This way, if you move forward in hiring, you’ll already know how they prefer to improve their skills and stay knowledgeable. You can supplement their way of learning once they are on board with your team. 

5. How do you handle receiving feedback? How does feedback impact your choices as a developer? 

This open-ended question aims to check whether a candidate can follow instructions and accept feedback. Note what you like and dislike about their answers and try to understand where they’re coming from. 

6. How do you implement automated testing in your JS code?

Web application testing is essential when building robust code. The best and most experienced developers understand the importance of automated testing and have the know-how to implement them.

Sample answer:

Automated testing is essential to produce a bug-free program. There are three ways to do them:

  • Unit testing
  • Functional testing
  • Integration testing

I usually use tools for automated testing, including Jest, Karma, Mocha, Cucumber, Casper, etc. 

7. Which JS frameworks do you have the most experience with? Why do you prefer these over other popular frameworks? 

It is important that developers are familiar or experienced in working with popular JavaScript-based frameworks and technologies. They should highlight which libraries or frameworks they’re familiar with. The specificity with which they compare frameworks will be a good indicator of the depth and breadth of their experience. 

8. What are the disadvantages of JavaScript?

There are always tradeoffs in software development using any web technology or programming language. Developers who are aware of these disadvantages are more likely to have a deeper understanding of the tools and technologies they are using.

Sample answer:

Although JavaScript is a very powerful and convenient programming language, it also has some disadvantages. One of the major issues of JS is that it has security vulnerabilities. Also, being a dynamically-typed language, it is prone to errors. Lastly, there are instances when JS code will run differently in different browsers. 

9. How do you resolve conflict with other team members?

In a software development team, conflicts are common. In fact, a team that produces many ideas, sometimes causing some conflict too, is a sign of a healthy team. Thus, every member must know how to communicate their ideas well to reduce and resolve potential conflicts.

10. Are you involved with any JavaScript or web development communities?

There are many communities in web development. Developers eager to learn and passionate about their craft are often active in one or more groups. 

Find the Best JavaScript Developers Here!

Recruiting the right talent for your software development team is the key to achieving successful projects. That said, finding great tech talent these days is no small feat! If you’re looking for JavaScript Developers, Full Scale has the right people for your business. 

Full Scale is an offshore software development center that specializes in helping businesses build world-class teams of developers and QA professionals quickly and affordably.

With our pool of qualified and experienced QA professionals, you can build a team quickly and affordably. Take a look at our recruitment and assessment process.

As the video shows, our developers are technically skilled and are also great communicators. They are great members who can instantly contribute to your project.


Hire a JavaScript Developer from Full Scale today!

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