Top 50 JavaScript Developer Interview Questions to Select the Best Candidate

For many years, JavaScript has been the go-to language for building modern and interactive websites. That makes it the most in-demand skill set, creating job opportunities for freshers and experienced professionals.

However, finding the right JavaScript developer can be tricky due to the constantly evolving nature of the language and its wide range of uses. In addition, there is a high demand for skilled JavaScript developers, which means there are more job openings than qualified candidates.

So, as an interviewer, it's important to ask JavaScript interview questions that assess the candidate's technical skills, problem-solving abilities, and understanding of JavaScript concepts. The questions should be designed to evaluate the candidate's knowledge of the language, as well as their ability to apply that knowledge to real-world situations.

Some key factors to keep in mind when designing interview questions for JavaScript developers include:

• Technical knowledge: The candidate should be able to demonstrate a strong understanding of the core concepts of JavaScript, including variables, data types, functions, and control structures.
• Problem-solving abilities: The questions should be designed to assess the candidate's ability to think critically and solve problems using JavaScript.
• Understanding of JavaScript frameworks: Depending on the role, it may be important to ask questions about popular JavaScript frameworks such as React, Angular, or Vue.js.
• Communication skills: It's important to ask questions that allow the candidate to explain their thought process and communicate their solutions effectively.
• Familiarity with best practices: Questions should also assess the candidate's knowledge of best practices in JavaScript development, including coding standards, performance optimization, and security considerations.

Overall, asking well-crafted JavaScript interview questions is crucial to identifying the best candidates for the job and ensuring that they have the necessary technical and problem-solving skills to excel in the role.

So, if you, too, are planning to hire JavaScript developers in 2023 for your team or company, this JavaScript developer interview questions guide will help you recruit intelligently.

JavaScript Developer Interview Questions for Experienced Developer

While conducting technical interviews, recruiters must ensure that candidates are proficient with front and back-end tools and possess enough abilities to finish projects. To help you out, we’ve compiled a list of the 50 top JavaScript developer interview questions, ranging from beginner to advanced. This set of JavaScript developer interview questions will thoroughly test your candidates’ potential.

1. What is a strict equality operator in JavaScript?

2. What are the structures in v that are considered looping structures?

3. What is the complete syntax of JSON.parse() method?

4. In JavaScript, which method is similar to the pop method?

5. How to get 1st January 1970 in a date object, the date from where time is gets calculated?

6. How can you create an array in JavaScript?

7. Write a Regular expression to validate an email address.

8. What are the different overloaded signature for drawImage() method?

9. What is the difference between Async/Await and Promise?

10. How do you create a new Object in JavaScript?

11. What are the advantages of using external JavaScript files?

12. What’s the difference between Var, Let, and Const keywords?

13. Name seven error types in JavaScript.

14. Give an example of practical implication of closure concept?

15. How will You create, read, and delete a cookie using JavaScript?

16. Explain what a call-back function is and provide a simple example.

17. What does Object. Create () method do?

18. Implement enqueue and dequeue using only two stacks.

19. How would you use a closure to create a private counter?

20. How to load an image in Canvas?

21. When would you use the bind function?

22. Write a recursive function that performs a binary search.

23. How to inherit from a class?

24. How do you remove duplicates from a JavaScript array?

25. How would you create a private variable in JavaScript?

Junior JavaScript Developer Interview Questions 

1. What is JavaScript?

2. What are the data types supported by JavaScript?

3. List some key features of JavaScript.

4. How can you create an object in JavaScript?

5. How do you add comments to JavaScript code?

6. Explain what a call back function is with a simple example

7. What is the purpose of the ‘This’ operator in JavaScript?

8. Name some of the built-in methods and the values returned by them.

9. How do you import all named exports from a JavaScript file?

10. How to create a cookie using JavaScript?

11. How to check if an object is an array or not? Provide some code.

12. What is the difference between Attributes and Property?

13. Implement enqueue and dequeue using only two stacks

14. List ways to access an HTML element in JavaScript code.

15. How to embed JavaScript code in an HTML file?

16. What is NaN in JavaScript?

17. Name the looping structures in JavaScript.

18. What is the difference between local and session storage?

19. What is the difference between the operators ‘== ‘and ‘=== ‘?

20. Provide some examples of non-Boolean value coercion to a Boolean one

21. How would you check if a number is an integer?

22. Given a string, reverse each word in the sentence

For example: Input:  Geeks for Geeks and Output: skeeG rof skeeG 

23. Explain call (), apply () and, bind () methods.

24. What is DOM? Give an example of how HTML code gets converted to DOM.

25. How can you Handle exceptions with JavaScript?

To assess technical and functional skills required by a competent JavaScript Developer, check out iMocha's coding skill tests library.
 

Tips to interview JavaScript Developers

1. Check the candidate’s portfolio

You can request previous work samples for a technical position like a JavaScript developer. A candidate’s portfolio will help you better understand the technologies they have worked on previously. It further explains their involvement in the overall project, which indicates their skills and knowledge.

For example, when hiring a JavaScript developer, you need to know if they have previously worked on both front and back-end development. With the help of a candidate’s portfolio, you can analyse their past skills and experience.

2. Assess JavaScript skills

Before hiring a JavaScript developer, it is essential to determine their area of expertise. This will help you make the right choice for the position you are trying to fill. With proper assessments in place, you will be able to determine the coding abilities of the potential candidate. This is done using a skills assessment platform like iMocha.  

iMocha is a skills assessment platform that enables you to make talent decisions. It offers the world’s most extensive skills library with over 2500+ skills, including coding, next-gen, app development, communication, etc.  

This platform quantifies recruiters of the applicants’ technical abilities and skills. To do this, it offers features like Live Coding Interview, Project-based assessments, AI-LogicBox, (which acts like a code-in-the-blanks format so candidates don’t have to start from scratch), asynchronous interviews, etc. With these features, you can determine candidates’ cultural fit, avoid making bad hires, handle high-volume hiring, eliminate biases, etc.

3. Evaluate the non-technical skills
Hiring a candidate for programming alone is not enough. A great JavaScript developer will possess much more than just the ability to code. Various other non-technical skills are just as crucial to success. That is why it is essential to evaluate the non-technical skills of a JavaScript developer during the interview to understand the candidate’s interpersonal and soft skills.

For example, A JavaScript developer with good communication skills will be able to communicate suggestions, ideas, and project progress to others in the team effectively.  

A few non-technical skills of a developer include:

• Communication skills
• Time management
• Teamwork
• Creativity
• Problem-solving skills

Conclusion

Hiring the right people for your development team is the key to achieving successful projects. With the help of JavaScript developer interview questions, you can ensure that the hiring process goes smoothly and successfully – allowing you to hire an excellent programming team to complete your project on time and within budget. 

Happy Hiring!

FAQ Reference

1. How do you interview a JavaScript developer?

Interviewing in tech is tricky because you must assess highly specialized skills to see great results. Fortunately, technology is evolving rapidly, and there are several tools that recruiters can use to streamline the process.

Here are a few ways to interview a JavaScript developer:

1. Technical assessments: A technical skills assessment evaluates the breadth of a candidate’s knowledge in their area of expertise.

2. Live coding challenges: A live coding challenge is a test where JavaScript candidates can solve problems via code. It allows you to gauge a candidate’s potential in a real-life scenario. Read on to this blog to know how you can assess & hire JavaScript developer with the help of iMocha's coding features

3. Take-home projects: Some companies allow candidates to complete a coding challenge from home within a given time. A take-home project will analyse a candidate’s critical thinking, problem-solving, and adaptability.

2. What to look for in a JavaScript Developer?

 A JavaScript developer is responsible for designing applications and software using Java. They carry out many roles, which are broadly categorized as front-end, back-end, or full-stack. 

Here are six things a JavaScript Developer should know:

• A solid understanding of code
• JavaScript developers should understand the difference between local and global scope.
• They must understand how JavaScript utilizes control flow to write error-free code.
• Identifying the type of error and finding the solution
• Basic understanding of Node.js
• An understanding of important software security model