JavaScript Coding Interview Questions: Resources and Challenges

JavaScript is the programming language most widely used to make web pages interactive—to engage readers with elements like a sign-up page, a chatbot, or a “refresh” button. The language is known and used by Computer Science professionals. That makes it, in turn, a chief focus of tech-firm hiring managers as well as engineering department executives involved in hiring.

JavaScript, in brief, is a text-based programming language. It has uses both on the Frontend (client side) and Backend (server side). Typically, HTML and CSS, for example, bring structure and style to web pages, while JavaScript brings user-interaction. By moving from a static to an interactive experience, JavaScript enables the page to respond to the user.

This language also has built-in frameworks in JavaScript code libraries that are pre-written code for developers to use in building web and mobile apps. Frontend frameworks include React, React Native, Angular, and Vue. Each has multiple uses as the advanced starting point for developing a finished product. PayPal, LinkedIn, Netflix, and Uber, for example, all use a JavaScript runtime environment.

Some reasons JavaScript is the most popular programming language: It is the only language native to the web browser. Getting started using some of its elements is quick even as the code is being learned. And, of course, the more widely used a programming language, the more incentive to learn it.

The traditional JavaScript coding interview is under pressure to change. Tech companies want to fill positions with engineers who are technically skilled — and that means able to fluently code in clean JavaScript. It also means demonstrating use of JavaScript to define and solve software development problems, for example, or installing an app on a webpage.

Unfortunately, the common telephone interview cannot assess JavaScript technical skill. Skills are demonstrated in use; what telephone interviewers or in-person interviewers can do by asking questions is gain an impression of the candidate’s JavaScript technical vocabulary, familiarity with applications, and report on projects completed.

Woven’s online coding challenges directly assess coding in the programming language being tested. Coding is in the context of job-related problem-solving situations. The challenges are geared to both the engineering role and the skill level required (for example, Mid/Senior Fullstack Developer, or Engineering Manager).

In the case of JavaScript, the focus of testing today is on ES6 (ECMAScript 2015), introduced in that year as the 6th version of the programming language. It is the most recent standardization of JavaScript.

JavaScript interview questions by topic

GitHub offers a list of ES6 interview questions. These are the first 10:

• Can you give an example of destructuring an object or an array?
• List out important features of es6.
• ES6 Template Literals offer a lot of flexibility in generating strings, can you give an example?
• What is the benefit of using the arrow syntax for a method in a constructor?
• What are fat arrow functions? When should you not use arrow functions in ES6?
• How does [sic] await and async works [sic] in es6?
• What are the benefits of using arrow functions over es5 function?
• What are the differences between ES6 class and ES5 function constructors?
• What are the benefits of using spread syntax and how is it different from rest syntax?
• What are the differences between variables created using let, var or constr?

These are examples of JavaScript screening questions or JavaScript interview questions. They are not JavaScript coding test questions.

When interviewing for higher-level engineering positions and technical skills, the interviewer might focus on a major functionality of JavaScript to test the depth of the candidate’s knowledge. Code Sample offers a list of “39 Best Object-Oriented JavaScript Questions and Answers.” Here are a few:

• What is Object in JavaScript?
• What is “this”? What is its value?
• What is a Closure and why are they so useful to us?
• Can you explain the difference between = = and = = =?
• Explain why asynchronous code is important in JavaScript.
• Tell me your JavaScript naming convention.
• What is Hoisted in JavaScript?
• What is the scope variable in JavaScript?
• How to achieve inheritance in JavaScript
• How to empty an array in JavaScript

Lists like this organized by theme or function can be found for almost any topic. As another example, GitHub offers JavaScript array interview practice.

JavaScript interview questions

Interviewers who want to focus on testing coding in JavaScript can find all the questions they need for white board or online using a coding editor. Educative offers this initial list of 10 coding tasks with hints and possible solutions:

1. Longest String in an Array. Write a function that accepts an array of strings. Return the longest string.
2. Most commonly used character in a string. Write a function that takes a string and returns the character that is most commonly used in the string.
3. Two strings are anagrams of each other. Create a function that takes in two strings as two parameters and returns a Boolean that indicates whether or not the first string is an anagram of the second string.
4. String permutation is Palindrome? Given a string, write a function that will return whether or not that string is a palindrome.
5. Balanced Brackets. Given a string possibly containing three types of braces ({}. []. ()), write a function that returns a Boolean indicating whether the given string contains a valid nesting of braces.
6. Armstrong Numbers. An Armstrong number is an n-digit number that is equal to the sum of the nthnthnth powers of its digits. Determine if the input is an Armstrong number. Return either true or false.
7. Sorting Objects. Given an array of objects, sort the objects by population size. Return the entire object.
8. Reverse a Linked List. Create a Node class and a LinkedList class with these methods:

• insertFirst(data)
• insertLast(data)
• getFirst()
• getLast()

9. Remove Kth-Node from Linked List. Using the Node and LinkedList classes that you created in the previous question, add methods to it so that, when given a kth-integer, you can delete the kthkthkth node from the linked list.

10. Create A Circular List. Given a linked list, return true if the list is circular, false if it is not.

Advanced JavaScript interview questions

Any productive test of technical skills, beginning with code writing, must consider the required skill level of the job. A test too easy will fail to screen out many candidates not operating at the level needed. Worse, a test above the top of the range required by the job will cause candidates to wonder if your company is unrealistic in expectations or tha you don’t understand the position.

Fullstack Cafe offers advanced JavaScript coding questions and answers “to kill your tech interview.” They begin with 25 questions to be solved with JavaScript coding. Here are the first 10:

• Explain equality in JavaScript.
• Explain Function.prototype.bind.
• Explain the difference between Object freeze () vs const.
• Give some examples of non-bulean coercion to a boolean one [sic].
• What are the differences between ES6 class and ES5 function constructors?
• What is IIFEs (Immediately Invoked Function Expressions)?
• What is generator in JS?
• What is a typical case of anonymous functions?
• When should I use arrow functions in ES6?
• When should we use generators in ES6?
• Explain the Prototype Design Pattern.

Returning to our earlier discussion of JavaScript interview questions topic wise—JavaScript interview questions for 5 years experience might ask about algorithms. That Js Dude offers these as “medium questions” about JavaScript algorithms:

• From two sorted array [sic] how would you find common number?
• From web page, how would u find similar words like rat, cat, bat and broom, groom etc.?
• Get the first 100-character long string from a big message but don’t cut the last word (word break problem).
• Find the max difference of elements from two sorted arrays with non-duplicate integer elements.
• Second symbol starting index Array of two symbols?
• Determine if a positive number can be expressed as a sum of two cubes.
• 4SUM?
• From an array of integers find 10 numbers closest to a given number.
• Find a rotation point of a sorted array.
• Finding three elements in an array whose sum is closest to a given number.
• Write a function to find the nearest link on a webpage given the mouse x,y coordinates.

The online community pays a surprising amount of attention to tricky JavaScript interview questions. Fullstack Cafe offers a list of 25. To take just a few examples:

• What is the difference between Anonymous and Named functions?
• What is the drawback of creating true private in JavaScript?
• What’s a typical use case for anonymous functions?

Woven’s coding challenges are our chief business—and our mission. We are not a question bank, but an assessment tool used for obtaining objective evidence of coding writing and other technical skills. Our assessment is inspired by a simulation of real-life coding challenges from tech firms that want to build top development teams with best available talent. That requires assessing the ability to take problems that must be defined, attacked with appropriate tools, and solved. It also requires technical communication by each member of the team.

JavaScript interview coding challenges

On the web, “JavaScript Coding Challenges” has several meanings. Sometimes it refers to organizations like Woven and our competitors, which provide tech firms with tests for coding skills. Some tests are free and some are available by subscription. Usually, however, the offer is the product itself (the test or challenge) and not services of this kind:

• Developing challenges customized for specific recruiting goals
• Exploring the right challenge for a given engineering role and level
• Administering the test as a step in screening candidates
• Scoring of the test by experienced engineers who interpret test results and generate a report and appropriate recommendations.
• Follow-up to provide candidates with objective reports on their relative performance on the test.

Another meaning of “JavaScript coding challenges” is the lists of coding questions and problems for interviews, like JavaScript exam questions and answers. Many of these are described as interview coding challenge examples—except that the traditional phone or in-person interview does not and cannot challenge coding skills. Neither skill in writing haiku nor skill in coding can be assessed without observing the skill in practice.

GitHub offers “JavaScript Modern Interview Code Challenges” by topic. The topics include Primitives, Functions, Objects, Collections, and Asynchronicity. Here are examples of some challenges:

• Design a Calculator interface for 2 number inputs which can perform sum, difference, product and dividend whenever invoked on the same interface.
• Design a private counter function which exposes increment and retrive [sic] functionalities.
• Write a polyfill for bind function.
• Write a function which will create a function bounded to the context like bind, but can be overridden when the context is set explicitly.
• Write a function which helps to achieve multiply(a)(b) and returns a product of a and b.
• Create a function which takes another function as an argument and makes it eligible for currying or partial application.
• Design a function which helps to do debouncing.
• Design a function which helps to do throttling
• Design an interface which limits the number of function calls by executing the function once for a given count of calls.
• Write a singleton function to create an object only once.

HTML/CSS, JavaScript coding questions

A “challenge” to testing for coding and other technical skills is targeting the tests to software development roles, and other computer engineering positions, in their commonly used program coding languages. And the same applies to testing the core engineering competencies (for example, debugging, Frontend development).

To take but one example, HTML/CSS tends to be used in Frontend website page creation, structuring, and presentation. JavaScript adds to the Frontend presentation all interactive features, from search boxes to refresh buttons. Python tends to be used for both client/interface and server-side programming. Thus, it is favored by Fullstack developers whose role is to ensure smooth, integrated connection of Backend and Frontend functions.

These are considerations that we take when creating coding challenges. Woven challenges are defined by the roles for which tech companies are recruiting. We’ve focused on nine essential positions required on the full computer-engineering development team:

• Mid/Senior Fullstack Engineer
• Junior/Mid Fullstack Engineer
• Engineering Manager
• SRE/DevOps Engineer
• Mid/Senior Frontend Engineer
• Junior/Mid Frontend Engineer
• Mid/Senior Backend Engineer
• Junior/Mid Backend Engineer
• Mid/Senior Generalist Engineer.

We build the skills profile for each position using a mix of core software development skills: debugging, technical communications, systems thinking, Backend Programming, and Frontend Programming.

These challenges can be presented in any preferred programming language, but all require clean and effective coding to define and solve the problems that your development team faces daily.

JavaScript coding questions for practice

Candidates seeking practice exercises for either the traditional telephone interview, in-person interview, or online coding challenge can find JavaScript coding questions in abundance.

W3Resource has a long list of JavaScript coding exercises. These are free resources for candidates who want to master the language:

• JavaScript Basic [ 150 Exercises with Solution ]
• JavaScript Fundamental (ES6 version) Part-I [ 150 Exercises with Solution ]
• JavaScript Fundamental (ES6 version) Part-II [ 116 Exercises with Solution ]
• JavaScript Functions [ 29 Exercises with Solution ]
• JavaScript Recursion [ 9 Exercises with Solution ]
• JavaScript Conditional Statements and loops [ 12 Exercises with Solution ]
• JavaScript Array [ 44 Exercises with Solution ]
• JavaScript Date [ 53 Exercises with Solution ]
• JavaScript String [ 49 Exercises with Solution ]
• JavaScript Math [ 53 Exercises with Solution ]
• JavaScript Validation with Regular expression [ 20 Exercises with Solution ]
• JavaScript HTML DOM [ 13 Exercises with Solution ]
• JavaScript Drawing [ 6 Exercises with Solution ]
• JavaScript Object [ 18 Exercises with Solution ]
• JavaScript Basic Validation without Regular expression [10 Exercises with Solution ]
• JavaScript Searching and Sorting Algorithm [24 Exercises with Solution ]

We can see that the arms race between big tech companies and job candidates is alive and well. There are unlimited question banks for potential interviewers and unlimited help for candidates to prepare for interviews. Overall, this is positive. Tech companies are seeking genuine assessment of technical skills to build the best possible development teams. And candidates motivated to improve their skills have access to unlimited resources.

For example, Hackerrank is an online site that offers tech firms information to fashion their own coding tests. These companies then administer the test to candidates online and can download the score results from Hackerrank instantly. The challenges that Hackerrank offers, ready-made, are organized around the most common engineering topics.

In contrast, Woven’s senior engineers work with your company to define the assessments that you need, select appropriate challenges, and customize them. You don’t need to create your own tests; our engineers refine and administer challenges based on your individual hiring requirements. This includes matching the challenges with the role you seek to fill and the level of skill required for that role.

We administer tests on behalf of your company to screen candidates. Then, our network of engineers scores and interprets the answers to job-related problem-solving scenarios. The assessment, which is done by at least two engineers, focuses not only on questions that are “right or wrong,” but what answers reveal about a candidate’s skills in defining problems, selecting tools, and developing solutions.

Our report and assessment includes recommendations, too. We follow up with a consultation to interpret results and project next steps.

Woven also reports to all candidate test-takers on their performance for professional development. The attention paid to candidates has resulted in a 90 percent acceptance rate when we ask candidates to take the challenge.

Hiring managers and engineers involved in recruiting can learn more about our approach by requesting a free trial. We are happy to answer questions or begin a discussion about your hiring goals.