JavaScript Interview Questions To Help Find Your Ideal Candidate

Requirements and Key Skills to Look for in a JavaScript Developer

Your perfect JavaScript candidate should combine those specific hard & soft skills to become a valuable team member. Here’s a list of characteristics you should look for in a JS developer.

Hard skills

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Coding. Since JavaScript is rich in technologies for front-end, back-end, and mobile development, you should pay attention to the developer’s knowledge in a particular area. JavaScript is represented by Node.js for back-end development, React and Vue for creating user interfaces, and React Native for writing mobile apps. A skilled JS developer should also be familiar with such technologies as jQuery, Angular, Next.js, and Ionic, etc. 

No matter what technologies a JS developer works with, their code should be clean, consistent, understandable for other colleagues, and maintainable. 

Testing. Although there is a separate role for software testing in IT companies, JS developers should also be able to test their code on their own. They usually can do it with unit tests that allow them to check code quality and prevent bugs early in the development process. Developers’ ability to run unit tests allows the whole team to be more productive, use resources effectively, and optimize development budgets.

Debugging. Bugs are a common occurrence in software development, so every JS developer should know how to fix them. This skill requires developers to be able to use different debugging programs and techniques. That’s why JavaScript questions interviewers ask should cover this skill, too.

Soft skills

An effective JavaScript developer is not only tech-savvy but also a great team member. As an employer, you probably want a warm supportive atmosphere in your team where everyone strives for success. Thus, you should pay attention to the following soft skills of a JS developer:

Communication skills. Although developers spend a major amount of time in front of their monitors writing code, they should be able to communicate effectively with all team members, including product/project managers, quality assurance engineers, UI/UX designers, and other developers. Good communication skills are crucial to ensure that software created by a JS developer meets all the requirements and works exactly how it should.

Problem-solving skills. Be it a bug that needs to be fixed or a contradiction with a manager on how to implement a particular functionality, developers should be able to handle such situations smoothly. Being part of a team, they should understand that such issues often affect the whole development process. Therefore, problem-solving is a skill you need to identify when you interview JavaScript developers.

Time management. Taking into account the fact that developers always work under deadlines, there’s no need to explain how crucial their ability to manage time is. You definitely want a person on your team who will be able to do the tasks on time, according to sprint planning and release dates.

Managerial skills

The career of JS developers doesn’t end at the “senior developer” point. Professionals who thrive for more can become team leaders. Thus, top JavaScript interview questions should touch upon the following topics if you’re looking at that JS developer for a future managerial position. 

Team management. It’s a core skill of a team leader since their main responsibility is to ensure effective teamwork. To succeed in this task, a candidate should boast great communication skills, be able to give and take constructive feedback, think strategically, and possess high emotional intelligence.

Planning. Closely connected to the previous point, planning is a crucial part of effective team management. A developer in a leading role should be able to plan sprints, set project milestones, define deadlines, and ensure that the team follows them.

Conflict-solving skills. Conflicts might appear between colleagues as well as the team and client. No matter the conflict’s nature, a team lead should understand different perspectives and be able to find the best solution without harming the project's success.

Core Interview Questions to Check Hard Skills

Interview JS questions vary depending on the level of the JavaScript developer. Below, you’ll find question examples to check hard skills of different seniority levels.

Questions for junior developers

1. What are the advantages of JavaScript over other web technologies?
2. What data types are there in JavaScript?
3. What does DOM mean in JavaScript?
4. What’s the difference between equality and strict equality operator in JS?
5. Differentiate "undefined" and "null" in JavaScript? When would you use each one?
6. Explain the purpose and usage of callbacks in JavaScript. How do they relate to functions like setTimeout and setInterval?
7. Describe the concept of closures in JavaScript and provide an example of how they can be useful.

Questions for middle developers

1. What is recursion in JavaScript?
2. What are promises in JavaScript?
3. Discuss common security vulnerabilities in JavaScript applications and how they can be mitigated. What is Cross-Site Scripting (XSS) and Cross-Site Request Forgery (CSRF)
4. Compare different state management approaches in front-end frameworks like React and Vue.js. When would you choose one over the other?
5. How do you handle dependencies in a JavaScript project?
6. Discuss the major features introduced in ECMAScript 6 (ES6) and later versions. How have these features improved JavaScript development?
7. Describe the differences between the 'apply', 'call', and 'bind' methods in JavaScript. Provide examples of when each would be used.

Questions for senior developers

1. Describe the architecture of a large-scale JavaScript application you've worked on. How did you ensure scalability, maintainability, and performance?
2. How do you ensure code quality in a JavaScript project? What coding standards and best practices do you follow?
3. Share examples of how you've optimized the performance of a JavaScript application, considering aspects like lazy loading, code splitting, and server-side rendering.
4. Explain your approach to error handling in a JavaScript application. How do you log and monitor errors in production?
5. Discuss your approach to designing APIs in a JavaScript project. How do you document APIs for internal and external stakeholders?
6. Explain the concept of "memoization" and how it can be applied in JavaScript for performance optimization.
7. Have you developed real-time applications using technologies like WebSockets or GraphQL subscriptions? Share your experience and challenges faced.

In addition to questions, you can also ask candidates to do JavaScript interview tests. These can be small coding tasks that demonstrate your candidates’ way of thinking and how they apply their knowledge in practice. For example, you might ask them to write a function to find the largest number in an array or implement a queue in JavaScript.

As a leading IT recruiter at Huntly, I’m responsible for the pre-screening of candidates during the initial stages of hiring process, which can also include test tasks. Delegate this recruitment part to our team and you will receive only qualified candidates who are highly interested in your JavaScript position.

Core Interview Questions to Check Soft Skills

As I have mentioned above, interviews questions shouldn’t be limited to the ones that check candidates’ hard skills. Soft skills are as important as hard ones if you want to find a top professional.

Here are some JavaScript job interview questions you might want to ask your candidates to learn more about their communication, problem-solving, time management, and decision-making skills, etc.

1. How would you prioritize several tasks with the same deadlines?
2. What would you do if you had to make a decision while your team lead is away for a vacation?
3. How do you handle criticism and feedback from your team/clients? 
4. What do you do if you don’t know how to solve a particular task?
5. Did you have mentorship experience when you had to support a junior developer? What did you like about it and what was your least favorite part?
6. How would you act if you and your team lead had different opinions on how to implement a particular functionality from a technical standpoint?
7. Was there a situation when you had a conflict inside your team? How did you handle it? 

Summary and Recommendations

Interview questions for JavaScript development roles include the ones to check candidates’ hard and soft skills. You should get insights into applicants’ professional and personal characteristics to make sure that your job offer goes to the best candidate. 

If you’re struggling to find an appropriate JavaScript developer to fill your open position, Huntly is here to help. By posting a vacancy on our platform, you can count on increasing the pipeline of relevant candidates by 10 times, thus multiplying the chance to hire a suitable candidate faster. As well, we ensure the high quality of tech talents we refer to you - 98% of specialists hired through Huntly pass a probation period.