JavaScript Interview Questions

Whether hiring for an entry-level web developer position or a web architect, asking the right JavaScript coding questions lets you assess the candidate’s depth of knowledge in core JavaScript concepts, problem-solving skills, and understanding of modern JavaScript practices. 

More than identifying which people in your pool of applicants can answer technical questions, these JavaScript interview questions also reveal who among them can apply their knowledge in real-world scenarios.

As you know, hiring the wrong person is tantamount to wasting money and training time. It also hurts productivity and can even demoralize current employees. 

By asking the right JavaScript interview questions from the start, you can select candidates who can bring practical value to your project.

Focusing on the right questions also minimizes bias based on first impressions. Well-designed JavaScript coding questions create a fair evaluation process.

JavaScript interview questions for beginners

Positions like junior web developers and content management system administrators often use basic JavaScript to add interactivity to web pages and for content editing. 

Non-technical roles like business analysts may need basic JavaScript to automate data manipulation tasks. Here are some basic JavaScript interview questions you can ask candidates applying for these roles:

JavaScript basics

• What is JavaScript?
• List some features of JavaScript.
• Who developed JavaScript, and what was its first name?
• List some of the advantages of JavaScript.
• List some of the disadvantages of JavaScript.
• Is JavaScript a case-sensitive language?
• How do you write a hello world example of JavaScript?
• How do you use an external JavaScript file?

Functions in JavaScript

• Define a named function in JavaScript.
• Name the types of functions.
• Define an anonymous function.
• Can an anonymous function be assigned to a variable?
• In JavaScript, what is an argument object?
• Define closure.

JavaScript in use

• What method is used to return the character from a specific index? 

JavaScript objects

• What is BOM (Browser Object Model)?
• What is DOM (Document Object Model)? What is the use of the document object?
• What is the use of the window object?

Differences and comparisons

• How are JavaScript and Jscript different?
• How are Java and JavaScript different?

Intermediate JavaScript interview questions

Are you hiring a front-end developer, a junior data analyst, a web app QA tester, or an e-commerce specialist? 

The JavaScript interview questions and coding exercises below are suitable for assessing candidates applying for these roles. 

They progress from basic JavaScript syntax and functions through data handling and operations to more advanced topics and interactions with the web environment. 

JavaScript basics and syntax

• How do you write a comment in JavaScript?
• How do you create a function in JavaScript?
• What is the actual name of JavaScript?

JavaScript data handling

• What are the different data types present in JavaScript?
• How are == and === different?
• What does the isNaN() function do?
• What is the output of 10+20+ “30” in JavaScript?
• What is the production of “10” +20+30 in JavaScript?
• What is the difference between an undefined value and a null value?

JavaScript objects and arrays

• How do you create objects in JavaScript?
• Describe how to create an array.

Web storage and events

• Can you explain which location cookies are typically stored on the hard disk?

Intermediate JavaScript concepts

• What is the use of the history object?
• How do you write HTML code dynamically using JavaScript?
• How do you write regular text code using JavaScript dynamically?
• What’s the difference between Client-side JavaScript and Server-side JavaScript?
• What’s the difference between event.preventDefault() and event.stopPropagation() methods in JavaScript?
• How can you determine if an event’s default behavior was prevented using an event in JavaScript?preventDefault() within a specific element? 
• Describe how to set the cursor to wait.

Advanced JavaScript Interview Questions

To test a candidate’s grasp of advanced JavaScript concepts, you need to cover

essential to complex aspects — data handling, user interaction, state management, and performance. 

The JavaScript interview questions below suit higher roles, including software engineers specializing in complex web apps and back-end systems, full-stack developers, web architects, and web-based game developers. 

You can also use them when interviewing data scientist applicants who need to know how to use JavaScript to deal with large datasets.

JavaScript fundamentals

• Are Java and JavaScript the same?
• What is negative infinity?
• What is this keyword in JavaScript?
• What are the falsy values in JavaScript, and how can we check if a value is falsy?
• What does hoisting mean in JavaScript?
• What is JavaScript’s strict mode, and how does it affect how your code runs?

JavaScript programming techniques

• How are exceptions in JavaScript handled?
• What is the requirement of debugging in JavaScript?
• What is the use of the debugger keyword in JavaScript?

Form and user interaction

• How do you submit a form using JavaScript by clicking a link?
• How do you validate a form/an email in JavaScript?
• How do you use JavaScript to detect the client machine’s OS?
• How do you change the background color of an HTML document using JavaScript?

Pop-ups and UI feedback

• Can you explain the different ways to create user interactions resembling JavaScript pop-up boxes?

Web state management

• How are the Session state and View state different? 

Performance considerations

• Is JavaScript faster than ASP script?

JavaScript objects and data types

• What are some of the standard functionalities of Math objects in JavaScript?
• What is the use of a Date object in JavaScript?
• What is the use of a Number object in JavaScript?
• What are some of the standard functionalities of a Boolean object in JavaScript?
• What is the use of a TypedArray object in JavaScript?
• What is the use of a Set object in JavaScript?
• What is the use of a WeakSet object in JavaScript?
• What is the use of a Map object in JavaScript?
• What are some of the standard functionalities of a WeakMap object in JavaScript?

Because JavaScript is constantly evolving, you need to regularly update this list of JavaScript coding questions and JavaScript interview questions to reflect the latest standards. 

Making your questions relevant and up-to-date lets you test a candidate’s knowledge of the current best practices and ultimately helps you hire someone who can add value to your projects.