JavaScript Developer: Common Interview Questions

As with anything else in the IT world, the JavaScript hiring process can take several weeks. The candidate will be tested on soft skills by recruiter and hard skills by possible team lead, they may also be asked to solve a problem or conduct a code review. So, how does a JavaScript developer interview go, and what are the challenges for both parties when communicating about a job?

Features of the JavaScript specialist stack

According to PYPL (PopularitY of Programming Language) Index, JavaScript is in 3rd position in US, UK, and India. It is also in the top five in Germany and France. Since JavaScript’s capabilities are wide and constantly evolving, the stack of such a developer may differ not only depending on its level, but also on the project.

What a JavaScript developer does:

  • Creates the client side of applications.
  • Works with AJAX, Comet, server applications.
  • Creates OS and application software for custom browser scripts.
  • Carries out automation of office applications.
  • Deals with the implementation of engines and widgets.

Thus, JavaScript interview questions and answers can be completely different, and follow from its tasks on the project.

Technical Interview Questions JS 

Staffing Partner has broad experience in hiring JavaScript specialists of any range. In 2021 only, we hired almost 100 such experts. Our background shows that each company can held a technical interview of a candidate with different approaches, but there are basic questions that are used in most interviews.

Junior developer

Since this kind of specialist usually has only basic knowledge, often not backed up by practice, the questions here concern the core with a little practice with examples.

General issues:

  • Description of OOP principles, methods, properties of objects, data types in JS.
  • What is map, filter, reduce?
  • Write options for tasks with add and/or debounce functions.

Questions about React and Redux:

  • Purpose of React and Redux.
  • Organization of routing.
  • General questions about Webpack, gulp, package.json, node.js.

Middle developer

A specialist at this level is expected to be able to perform most tasks and should be able to work without contacting a team lead for about a week.

General issues

  • What types of tests are there, what libraries are used for this?
  • What is XSS and HTTP request, how are they used?
  • Characteristics of Observer, Pub / Sub patterns.
  • Data types, operators, prototypes, and methods in JS.

Knowledge of functions

  • What is memoization?
  • Description of the main functions.
  • The difference between function and arrow function.

Questions about front-end and layout

  • Can the performance of a web page be optimized?
  • What are the units of measurement, and what are their characteristics?
  • Description and examples of CSS variables.
  • Work with customization, rendering, and templating.

Angular and/or React Questions

  • Description of the work of custom injectors.
  • What is a Renderer service and native methods, when are they applied?
  • Application of the Virtual DOM algorithm.
  • Enumeration of control libraries to choose from.

Backend and databases

  • Characteristics of Node.js and description of the main frameworks.
  • Monoliths and microservices: difference, advantages, examples.
  • Differences between SQL and NoSQL, solving problems according to the specified parameters.

Additional tools

  • Application of JSON and its characteristics.
  • What is and where are npm install and npm ci used?
  • How is the modular connection of scripts, with examples.

Practical tasks

Implementing an array method or writing functions

Senior developer

A specialist who is able to manage processes and build the architecture of the development process.

General issues

  • General knowledge in TDD and BDD.
  • Technology stack for project implementation (examples are selected individually).
  • Which frameworks are the most popular and why? Application cases.
  • Description of popular patterns and regular expressions with examples.

Front-end and knowledge of Angular and/or React

  • Description of how requestAnimationFrame works.
  • Methods to avoid loading cached script and style files?
  • What are custom decorators, how do I apply them?
  • Explain what is the Virtual DOM.
  • Is there a difference between createRef and useRef?
  • Analysis of the sample code (provided by the interviewer).
  • Description of the implementation of features at the choice of the interviewer.

Backend and databases

  • Description of RDS and application examples.
  • Description of cases of occurrence of SQL Injections. Can they be avoided?
  • How to properly design a cluster on MongoDB?
  • Description of the basic principles of GraphQL.

Additional tools

  • Description of the git-flow methodology.
  • What does it mean to create squash commits during rebase?
  • General understanding and practical applying of CI / CD.
  • How to set up a deployment for multiple environments?

JavaScript tasks at the interview

Tasks JavaScript interviewers can provide differs from company to company. E.g. it can be implementing an asynchronous method, function, or creating a toggle component.

It should be remembered that in IT companies communication and analytical skills, dedication, and high motivation for learning, as well as the ability to look for new approaches in solutions, are well appreciated. Another frequent requirement is knowledge of a foreign language.

Please be aware that the lists of questions in the introductory and technical interviews can significantly vary from company to company. But with a good knowledge of the bark and honesty of the candidate, any interview will be successful. As for the interview evaluating a candidate’s soft skills, we’ll talk about that next time.

If you need to hire a JavaScript developer for your company effortlessly, contact StaffingPartner to get the job done within 1 month.

Read also: How to Hire a Java Developer; How to Hire Expert Python Developers; How to Hire Expert DevOps Engineers?

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