30 JavaScript Interview Questions To Help Find Your Ideal Candidate

JavaScript is one of the most widely-used scripting languages today. This is why  developers who are adept at this technology are highly sought-after all over the world.

Hiring a well-qualified JavaScript developer can be tricky due to high demand and steep competition in this field. So you’re going to need someone with the right technical skills, experience, and soft skills to ensure the right fit.

To find the right JavaScript developer for your project, you’re going to have to ask the right questions. Quizzing candidates can be a good way to not only assess their skills and knowledge about this programming language but also get a glimpse of how they solve potential problems they might encounter while working on your project.

In this blog, we’ll be sharing with you some important interview questions you need to ask a developer to get to know their skills, experience, and how they work. We’ll also be including some of the answers you should be looking for.  Let’s dive in!

Introductory Questions

The goal of asking introductory questions is to get to know a candidate a little better and not to test their technical skills. Their answers give you some insight on how they react, think, and would potentially fit into your organization.

Some of the answers to these questions will undeniably vary from one interviewee to the next. However, you’re not always looking for right or wrong answers here. Your objective is to get in a candidate comfortable enough while they introduce themselves as a professional. These JavaScript interview questions can help you out:

1. What’s the Most Exciting or Interesting Aspect of Javascript Coding for You?

2. What’s Your Preferred Development Environment? Why Do You Use a Specific Operating System, Ide, and Terminal in Your Work?

Asking this question helps you determine upfront if they’re using the same platforms as you.

3. What Resources, Tools, or Platforms Do You Use to Learn About the Latest Development and Design Trends?

This question gives you an idea of how a candidate pursues further education.

4. What Are the First Five Steps You Take When Creating a Web Page?

5. What Is a Recent Technical Challenge You’ve Faced and How Did You Resolve It?

6. What Programming Paradigms Do You Use to Increase the Maintainability of Your Code?

Here, you should be looking for answers such as functional programming or test-driven development. This is an important question especially if you’re hiring a freelance developer as it gives you some insight on how they keep their projects relevant, usable, and profitable over time.

7. If You Joined a Development Team That Used Tabs but You Used Spaces, What Would You Do?

This question tests a developer’s ability to overcome differences in preferences using the right tools. The candidate should recommend using a standard formatting tool so everyone’s code will look the same when pushed to the repository.

Questions About Specific Skills

The skills you’re looking for in a JavaScript developer should always depend on their role in the project. So the questions you ask should be different for junior and senior developers.

For junior developers, it may be enough to look for foundational JavaScript knowledge, basic HTML skills, and non-technical skill such as learning on the job, receiving and responding to feedback, and communication. Some JavaScript interview questions you can ask include:

8. What is JavaScript?

A candidate should be able to state that it is an object-based, dynamically-typed, weakly typed, interpreted, multi-paradigm programming language. Furthermore, he or she should be able to mention that it is a core web technology (alongside HTML and CSS) that started out as a client-side scripting language but can now be used server-side.

9. What Are the Data Types in JavaScript?

The answers should be: Number, String, Boolean, Function, Object, and Undefined.

10. What’s the Difference Between Undeclared and Undefined Variables?

An undeclared variable has not been declared in the program and therefore does not exist. It will result in a runtime error if a JavaScript program tries to read it.

On the other hand, undefined variable has been declared be has no assigned value yet. There won’t be an error if a JavaScript program tries to read it. Instead, an undefined value will be returned.

11. What is Dynamic Typing?

 This means that the type of variables can change at runtime.

12. What are JavaScript Callback Functions?

A callback function is a function that is called after another function has finished executing.

13. How Would You Learn About a New Javascript Library?

The answer to this question may vary. What you’re looking for here is how a candidate approaches further learning and staying updated in the changes in JavaScript.

14. Describe a Time When You Received Feedback on a Programing Task and How You It Helped You Become a Better Programmer?

On the other hand, when you interviewing candidates for a senior developer position, you should be looking for expert JavaScript knowledge, Namespacing, testing JavaScript applications, debugging, and mentoring inexperienced group members. You can ask these questions:

15. What Are the Advantages and Disadvantages of Javascript?

For this question, you’re looking at a candidate’s understanding of limitations or tradeoffs of web technology.

The advantages of JavaScript include:

• Interoperability with other languages

• The wide array of tools, libraries, and frameworks available

• Versatility

• Ability to be used as a server-side language using Node.js
• Ability to provide interactive elements and interfaces to web pages

Meanwhile, the disadvantages of JavaScript include:

• Security vulnerabilities
• Susceptibility to errors due to dynamic typing
• It may run differently on different browsers

16. What Is ‘This’ Keyword in Javascript and How Do You Use It?

In JavaScript, ‘this’ is a keyword that refers to the object from where it is called. A candidate should be able to discuss about call, bind, and apply in their answer.

17. What Are Closures and When Are They Used in Javascript?

A closure is a locally-declared variable that is related to a function. It stays in memory after the function has returned.

18. Why is Namespacing Important in JavaScript?

Namespacing is important because it helps avoid naming conflicts, logically separate code, and make the code more usable.

19. How Would You Implement Automated Testing on Javascript Code?

A candidate should be familiar with and implement different types of testing such as unit testing, integration testing, and UI/Functional testing. A candidate should be able to recommend tools to use such as Ava, Protractor, Phantom, Chai, and more.

20. What Are Your Favorite Frameworks and Technology Stacks for Javascript and Why?

Again, this answers to this question will vary. It can give you an idea of a candidate’s familiarity and degree of experience using these tools.

21. What Design Patterns and Architecture Have You Used in Building Previous Projects?

If you’re looking for a senior developer who will be part of the design process of your application, it’s important to know their experience working with software architecture.

22. How Do You Approach Difficult Errors in Web Applications?

Bugs and errors are common when writing code so you need to understand how a candidate approaches them. Ask them to describe a time when they encountered a particularly difficult error in a project. Ask them about the debugging tools they used as well as what they learned from the experience.

23. If You Could Use Any Tool to Build Our Application, What Would You Use?

Apart from getting a glimpse of how a candidate likes to code, this question also helps determine if he or she takes the time to understand the task first.

24. If You Were to Review or Check Another Group Member’s Code, What Would You Look For?

Senior developers may need to work with less experienced developers who may be prone to making mistakes. The candidate could mention aspects such as functionality, readability, style, conventions, and security flaws.

Questions About Experience

One of the most crucial factors you need to consider when interviewing JavaScript programmers is their relevant experience. A candidate who has worked on a project that is similar to yours can be an invaluable part of your project.

They can share best practices they’ve learned from past projects to ensure the successful development of your website or application. Here are JavaScript interview questions you may want to ask a candidate:

25. What’s your Experience Using JavaScript?

Let them recount past projects and clients they’ve worked with. It’s important to ask if they’ve worked on projects similar to yours.

26. How Long Have You Been a Programmer and How Long Have You Been Using Javascript?

27. What’s Your Most Recent Successful Javascript Project? or What Javascript Are You Most Proud of?

Let them go into detail about their past projects, how they addressed errors and issues, and what they’ve learned from that experience.

28. Was There a Time You Did a Project Using Javascript That Didn’t Work Out? What Happened and Were You Able to Resolve It?

29. What Applications Have You Used Javascript for?

Ask the candidate if they’ve coded different projects like eCommerce websites, user interfaces, URL encoding, or event delegation.

30. Are You Certified in Coding Languages or Practices?

Technology evolves constantly. A great programmer has the initiative to stay updated so don’t forget to ask about their education that supports their work as a JavaScript programmer.

Conclusion

Hiring the ideal candidate for a JavaScript developer position may not always be a simple task. You need to make sure that the person you’re bringing onboard is a great fit.

With the help of the JavaScript interview questions we mentioned above, you can make the hiring process run a little more smoothly. By the end of it, hopefully you’ve found the best match for you.

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