JavaScript Developer Interview Questions: How to Prepare

JavaScript has been around a long time, and it’s used everywhere. That’s one of the first things that Patrick Hubbard, “Head Geek” at software-development firm SolarWinds, points out when talking about JavaScript developers, and it’s something he recommends job applicants to keep in mind when interviewing for a JavaScript developer position.

“Because it is so pervasive and is in so many places, the usefulness of it is pretty broad, and it’s easy to just assume that all jobs of a particular ilk are similar to the one you have,” he said. “But one of the things to remember about JavaScript is the chances of any two organizations using it the exact same way are low.”

Therefore, Hubbard continued, it’s good to know your JavaScript history, and come prepared to any interview with questions of your own. Not only will that help you get a feel for the organization, but it prods your potential employer to talk about what they expect from their developers.

If you’re relatively new to JavaScript—or if you need to scrape the rust off your skills—check out hackr.io, which lists a variety of courses and tutorials for various languages. Mozilla’s site features a very nice rundown of the language’s basics, just in case you need to review concepts such as comments, operators, variables, and other elements.

JavaScript.info also offers an extensive walkthrough of fundamentals, including the ever-popular “Hello, world!” If you’re not feeling wholly confident in your JavaScript skills, it’s probably worth clicking through these sites’ various links the week before your big interview.

Experience-Related JavaScript Questions

According to Burning Glass, which collects and analyzes millions of job postings from across the country, most employers want their JavaScript developers to boast a variety of skills beyond “just” JavaScript. For example, AngularJS, Java, and Node.js are frequently cited in job postings.

In addition, companies are very interested in JavaScript developers possessing “soft skills” such as teamwork and communication, which makes sense—after all, you’re often joining a team of other developers, and all of you need to work together effectively. Check out the full rundown:

“If the applicant learns some things about how JavaScript is used in a way they haven’t used it before, but now they have read about it, it allows them to be more prepared and achieve the holy grail of the interview process, which is to field the question, and then turn around and ask a question of their own,” Hubbard said. “The most flattering thing you can do is get somebody talking about themselves.”

With that in mind, it seems likely that you’ll end up fielding questions from any JavaScript interviewer about your approach to JavaScript as a language; these questions may be more abstract and technical, or may require you to discuss your experience:  

  • Have you ever instrumented applications to improve quality over time?
  • How do you choose your frameworks, and how will you react if we refuse to replace something you dislike?

Hubbard likes to ask questions ranging from security management to team-building skills. Skill-sets can be easily gleaned via a test or a whiteboarding session; more important is how the candidate will fit into company culture.

“I try to ask questions more along the lines of [what] a technical product manager would ask when trying to determine dates and development costs,” Hubbard said. “I need to know if the candidate is going to have an understanding of what the business needs are if they’re working on their own.”

Here are some potential interview questions along those lines:

  • Tell me about an experience when a style guide got in the way?
  • What’s the biggest surprise you’ve found from production data that was not exposed in tests?

JavaScript Developer Maturity

“This is an opportunity to get into how they work with a team that had some frustrating habits,” Hubbard explained. “Another set of questions I like to ask concerns developer maturity—over time with developers, it’s more about what you don’t do. Are they focused on the problem, or focused on building something cool?”

Which leads to questions along these lines:

  • Tell me about the most awesome platform you’ve ever considered, and that you’re glad you didn’t wind up building. Why didn’t you build it, and what did you choose instead?
  • What do you do when you and another team member ID a security concern in code?

Hubbard said he also likes to ask questions that make interviewers think about the philosophy of which languages they use and why: “If you’re being hired as a developer for a particular language, and if you sound passionate about the language and radiate an understanding of appropriateness and have a sense of where it’s limitations and best assets are, they’re know they’ve got someone who really understands why that technology was selected.”

According to Burning Glass, JavaScript developer positions are expected to grow 14.9 percent over the next decade; current time to fill roles, which is generally viewed as a barometer of employer demand, is 41 days (which is pretty high). In other words, if you’re interested in becoming a developer, learning JavaScript is a pretty good move—there is clearly demand for it.