15 JavaScript Interview Questions and Answers You should Know

Hello!

JavaScript remains one of the most versatile programming languages for building dynamic websites and interactive applications. According to the Stack Overflow 2026 survey, it continues to be used by close to 65% of developers worldwide. At Reintech, the majority of our prescreened specialists actively leverage JavaScript to deliver outstanding results for clients across industries.

Why JavaScript Skills Matter in 2026

Businesses today actively seek skilled JavaScript professionals to maintain a competitive advantage in the digital space. In turn, developers benefit from competitive compensation packages and clear pathways for career advancement. Yet, both hiring managers and candidates must approach the interview process strategically—employers need reliable ways to evaluate real expertise, while developers must demonstrate both technical depth and practical problem-solving ability.

15 JavaScript Interview Questions

Below you will find 15 carefully selected JavaScript interview questions with concise, practical answers. Use them to assess candidates effectively when you hire JavaScript developers.

1. What do you mean by event delegation?

Event delegation is a powerful technique that lets you manage events more efficiently. Instead of attaching listeners to every individual element, you add a single listener to a parent container and use the .target property of the event object to identify which child element triggered the event. This approach reduces memory usage and improves performance, especially in dynamic interfaces where elements are frequently added or removed.

2. What is the use of ECMAScript?

ECMAScript serves as the official standard that defines the rules and specifications for scripting languages. JavaScript fully adheres to this standard, ensuring consistency and interoperability across different environments and engines.

3. When should you use prototypal inheritance?

Prototypal inheritance is particularly useful when functional programming or modular patterns are not suitable. It enables flexible composition patterns—such as “can-do,” “uses-a,” or “has-a” relationships—rather than the stricter “is-a” hierarchy of classical inheritance. Different forms of prototypal inheritance can be applied depending on the specific requirements of the project.

4. What is the use of strict mode in JavaScript?

Strict mode helps developers write more secure and reliable code by enabling additional error checks and surfacing hidden bugs early. In many cases, strict-mode code executes faster. It also disables outdated or poorly designed language features, encouraging cleaner, future-proof development practices.

5. How can you delete a cookie with JavaScript?

To delete a cookie, simply set its expiration date to a point in the past. This forces the browser to discard the cookie immediately. In certain browsers, you may also need to specify the correct cookie path for the deletion to take effect.

6. What is the difference between one-way data flow and two-way data binding?

One-way data flow ensures that data moves in a single direction, making the application state easier to understand and debug. The model remains the single source of truth, and only it can update the application state.

Two-way data binding creates a dynamic connection between the model and the user interface. Any change in the model automatically updates the UI, and any user input in the UI updates the model in real time.

7. What do you mean by higher-order function? Can you give some examples?

A higher-order function either accepts another function as an argument, returns a function as its result, or both. JavaScript includes several built-in higher-order functions that are widely used in modern development, such as map(), filter(), and reduce().

8. What are the two types of typed language?

Programming languages are generally classified as either statically typed or dynamically typed. Statically typed languages require variables to be declared with a specific type that cannot change. Dynamically typed languages allow variables to hold values of any type at runtime. In both cases, the type is associated with the value rather than the variable itself.

9. What are the benefits of microservice architectures?

Microservice architecture structures an application as a collection of small, independent services. Because each service operates autonomously, the system becomes easier to maintain, scale, and update. Teams can modify or deploy individual services without risking the stability of the entire application.

10. What is the use of the prompt box?

A prompt box displays a dialog that requests user input through a text field. Developers can include a message and buttons such as “Accept” or “Cancel.” The user must provide input before proceeding further on the page.

11. What are the different types of error name values in JavaScript?

JavaScript defines six standard error name values: URIError, TypeError, SyntaxError, ReferenceError, RangeError, and EvalError.

Thank you!
Join us on social networks!
See you!