JavaScript Online Coding Tests

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Whether you are a hiring team looking for help assessing the skills of your JS candidates or you are a JavaScript Developer looking to practice some Javascript online coding tests, Geektastic can help.

We have en extensive range of JavaScript coding tests to suit all levels of software engineer. We cover all the main frameworks and libraries.

This article will cover exactly what a JavaScript online coding test is, why they are used and what they should cover. If you are practicing your JS skills we provide some top tips for improving your performance.

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What is a JavaScript Online Coding Test?

Some companies will choose to devise their own tests. This has the advantage of being bespoke to the company. They can make any problems related to their specific challenges or tech stack. This tailored approach has its obvious benefits. However, as a candidate, the experience can be a little clunky and even frustrating. Often, you won’t know if or when your JS coding test has been reviewed and there may be no mechanism for feedback. Of course that’s where Geektastic is different. We have emails that notify the hiring team and the candidate when the challenge has been reviewed allowing both parties to view the review and even write their own respective comments on the review.

As developers, unlike many other jobs that rely solely on soft skills, we are in the unfortunate position of having a skill set that can be directly tested.

At its core that’s what a JavaScript online coding test is, a way to measure your own or someone else’s JavaScript skills. These challenges / tests are typically sent by a prospective employer or sometimes an external recruiter to job applicants, so that prospective JavaScript developers can be compared side by side.

With online javascript programming tests, this issue is compounded. At the extreme ends, you’ll find junior developers being asked to work for a week on building an application from scratch (which we would never do at Geektastic), or you’ll have senior developers being asked multiple-choice questions about how to declare a variable.

It’s for these reasons and more that most companies tend to opt for an online coding challenge platform like Geektastic. With platforms like ours, companies can select the appropriate test for the appropriate level. Not to mention, they don’t have to manually review every test. This is done by our team of expert developers. This means as a developer, you can be assured that you will receive the feedback you require to improve for the next test.

So what will they test? A JavaScript online coding challenge can be used to test almost any aspect of your development skills. You can find tests that cover the whole spectrum of JavaScript tools and frameworks, including:

  • ReactJS
  • React Native
  • Angular
  • Vue
  • Node.js
  • TypeScript
  • Express
  • Next
  • Ember

And more!

You’ll find tests that cover the most fundamental concepts, such as:

  • The difference between a string and an array
  • How to declare a variable
  • Basic arithmetic
  • Functions
  • Loops

Right the way through to more advanced concepts such as:

  • Closures
  • DOM manipulation
  • Asychronicity
  • Arrow functions
  • Functional programming
  • Using Object Literals to pass optional arguments

That’s a wide variety, and when it comes to how you will be tested, the methods can be almost as wide-ranging.

If any of those advanced concepts seemed unfamiliar to you, here is a quick refresher:


Closures can be an alien concept to many developers. According to MDN a closure is “the combination of a function bundled together (enclosed) with references to its surrounding state (the lexical environment). In other words, a closure gives you access to an outer function’s scope from an inner function. In JavaScript, closures are created every time a function is created, at function creation time.”

DOM manipulation

DOM manipulation is an important concept for any developer. By manipulating the Document Object Model you can achieve a variety of effects, such as adding elements to the page, modify the HTML of an element, modify element attributes, modify element classes and more. If you’d like to learn more about manipulating the DOM, a good place to start would be the MDN documentation or this video by Web Dev Simplified.


Javascript is a single threaded programming language, meaning only one instruction is being processed at any one time. Typically this happens in a synchronous manner, meaning one thing happens after another. However, a number of instructions could block the main thread, leaving the end users with a slow experience. Think about your code that may need to fetch a large image from another server for example. By using asynchronous Javascript such as promises, callbacks and async/await, we can ensure that our code is not render blocking, thus improving the user experience.

For more on asynchronous Javascript, check out this article by Sukjhinder Arora.

Want to test your JavaScript skills and be reviewed by one of our expert review team?


Functional programming

Functional programming in Javascript has grown massively in popularity in recent years.

It is a coding paradigm (like that of object oriented programming) which you will need to become familiar with if you are to land a job with certain companies.

The fundamental concepts of functional programming are:

It involves avoiding shared state, mutable data, and side-effects. Functional programming is declarative rather than imperative, and application state flows through pure functions.

Of course a detailed tutorial on functional programming is outside the scope of this piece. However a good place to start is’s article on the subject

How will you be tested?

Companies may employ some or all of the following to test your skills:

  • Multiple-choice questions
  • Small scale, end to end application builds
  • Debugging challenges
  • Algorithmic quizzes
  • Real world sample problems

Why are they used

Online coding challenges have become increasingly popular over the years, with more and more employers leaning on them to aid their hiring decisions, and for good reason.

This is amplified with Javascript online coding tests specifically. As JavaScript is the world’s most popular programming language, companies will receive more applications for these roles than other development roles. Specifically, junior vacancies, which will have a higher volume of applicants still, and with a lack of experience on the CV it can be hard to gauge who has the necessary skills.

Online coding challenges allow employers to pit these applicants against one another from a technical standpoint to see who is best suited to the role. This has its evident advantages at the junior level, but is no less important for senior hires too. With these hires it is critical to hire correctly given the broader scope of responsibility.

But aside from the fairly obvious reason of gauging skill level, why else might an employer use an online coding test to vet applicants?

One such reason is to help eliminate or reduce unconscious bias from their hiring process. While we wish it weren’t the case, most people carry around with them preconceptions of certain groups of people, and they often don’t realise the subtle impact this can have on their hiring decisions. By using an online coding test, an employer can get an objective assessment - comparing apples to apples, enabling them to pick the most suitable applicants for the role without being biased by any preconceptions.

Giving everyone a fair shot is at the core of why many companies use these challenges and tests. As these are often used early on in the interview process, they can be used to allow everyone a fair shot at demonstrating their skill. Whereas, if they were to spend hours interviewing each applicant, they simply may not have enough time to see everyone.

That brings us to another reason these javascript test questions have become so popular. They bring speed and efficiency to the hiring process. This is beneficial for both you as the applicant and the hirer. By eliminating endless laborious technical interviews and reviews, companies can drastically speed up the process. This enables them to make a fast and effective hire, freeing up senior developers / hiring managers time to focus on other tasks, and it allows you to speed up your job hunt!

Finally, another fantastic benefit to online coding tests is organisations can use them to map out a development plan for any future hires. No one is expecting you to get 100% on any test, regardless of how experienced you are. We all use Google and there is always more to learn. By looking at areas of the test you were less comfortable with, a savvy employer can use the results of an online coding test to build a development plan for your future.

How they can benefit you

Believe it or not, taking a JavaScript online coding test can benefit you in more ways than simply landing a specific job. With Geektastic you can complete a JavaScript programming test, gauge your performance against other JavaScript developers, and then be shown to potential employers. This will widen your pool of opportunities. You can even put your test scores or rankings on your CV to show to prospective employers.

But aside from landing a job, you can also use coding tests to improve your skills as a developer. You never improve if you don’t challenge yourself and this can be an excellent push to learn, get feedback and improve as a developer.

We also mentioned some of the benefits to employers that it’s worth highlighting will benefit you as well. A faster, more efficient hiring process, timely feedback and the removal of unconscious bias should all improve your overall experience.

What to expect during a Javascript Coding Test

So, we know what a JavaScript online coding test is, what might be covered, and how they can be useful for your career. But what exactly can you expect when you sit down in front of your computer to complete one of these tests?

As we mentioned earlier, these coding challenges can take a variety of formats and cover a wide range of topics. Even if you are interviewing for a Javascript Developer position, there is a possibility that you will be tested on ancillary skills. The best way to get a feel for what to expect is to simply ask ahead of time. You may be very surprised at how much information you can get by simply asking. At a basic level, most companies and recruiters will always tell you the format. However, it’s not uncommon for companies to disclose the topics that will be covered. Sometimes these “topics” become rather specific, pointing to exact areas you’ll want to brush up on before the test. In fact sometimes asking “what areas should I brush up on before this test” will reveal far more information than you may expect.

With all that said, we can give you an insight into how the Geektastic platform works, should you encounter one of our online coding challenges.

Tips to excel:

  • Prepare

As Benjamin Franklin once wrote, “If you fail to plan, you are planning to fail”. This applies perfectly to online coding tests. Preparation is your first step. If asking your recruiter or HR contact what the test will cover hasn’t yielded significant results, review the job description in detail. It’s likely that you will be tested around these requirements, and should you be tested on anything else, it’s unlikely to impact your results significantly.

Also, while it may seem obvious, take note of the seniority of the role you are applying for. If you’re applying for an entry level position, there will be little benefit in brushing up on highly advanced concepts.

  • Revise

Unfortunately, if you want to perform your best, this can’t be avoided. Brush up on the essential concepts you have identified. Luckily many tests are “open-book” which means you will have access to Google and other resources. This will minimise the amount of cramming you will need to do. These challenges aren’t designed to test rote memorisation but more problem-solving skills. That said, you can’t avoid the fact that you need the requisite problem solving toolkit already.

  • Eliminate distractions

Ensure your environment is free from any distractions. These can be both physical, such as making sure any pets, children and significant others are in another room. Or indeed they can be digital. Put your phone on, do not disturb, make sure you close down, Slack, WhatsApp or any other applications on your computer that may cause you to get distracted. This may seem like a relatively small point, but the human brain doesn’t cope well with “task-switching”. These distractions can cause a serious dent to your productivity. That goes for the working day as well as tests!

  • Timing

Having a grasp of the time constraints, if any, beforehand will help guide your approach. Many coding tests are untimed. You’ll still want to complete these promptly to show you are swift and proactive, and sometimes to give you an edge on other candidates. However, with untimed tests, there really is no excuse for typos, missing commas or sloppy code. Never put speed ahead of accuracy in an untimed test environment.

With a timed test on the other hand, you will need to prioritise. Focus on problems that you find comfortable first before returning to more challenging problems that will take up more of your time. Try to avoid stressing or panicking. If you know your test will be timed, perhaps try some similarly timed practice tests to get a feel for how much time you will have on the day.

  • Understand how you will be assessed

Understanding how you will be assessed should also have some bearing on how you approach the test. Some platforms will automatically score your results. This means you’ll need to put extra emphasis on accuracy. Make sure there are no spelling mistakes or missing commas that could derail your test.

On the flip side, if you are working with a platform like Geektastic that uses a team of highly trained developers to manually review your code, while accuracy is still important, you can put more effort into commenting your code to show your thought process or creative problem solving skills.

Moving forward with your career

We hope this run down has given you a good insight into what to expect from a JavaScript online coding test, how to prepare for one and some excellent ways you can use these to further your career. If you’d like to read more around this area, we have some excellent resources on our blog, or if you’d like to try your hand at our free JavaScript challenges, check them out by registering here.

Regardless of where you go next, good luck on your journey as a developer and good luck with your next challenge!

We have coding challenges suitable for all levels and carefully tuned to ensure that they will always return useful feedback.

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Looking to find out more about take-home code challenges and what makes a good challenge?

Check out of page where we talk about take-home code challenges