How to Hire a JavaScript Developer: Skills Checklist and Red Flags
Hiring a skilled JavaScript developer is essential whether you’re building a front-end interface, a complex single-page app, or full-stack solutions. But with so many resumes out there, GitHub links, and self-taught freelancers winging it with AI, how do you separate the pros from people who might not have all the skills?
In this article, we’ll go through a comprehensive checklist of necessary technical skills to look for, along with warning signs that indicate a potentially bad hire.
1. The must-have core JavaScript skills
Before getting into frameworks and libraries, make sure your candidate has a rock solid understanding of JavaScript itself. They should meet the following minimum requirements:
2. Experience with front-end frameworks is a must
JavaScript projects will need a web developer who has experience with at least one front-end framework like React, Next.js, Vue, or AngularJS (Angular). Each framework comes with different pros and cons for projects, and they are not all equal.
In addition to knowing at least one framework, a good developer should also know the framework best suited for your project. For instance, if you need integration with existing tech, Vue can be seamlessly integrated into your current systems without disruption, but other frameworks may not be ideal. If a developer doesn’t know the ideal framework, they shouldn’t take on the project.
Now let’s look at what each type of developer should know:
React developers: React developers need to know core concepts like hooks, component lifecycle, context API, and state management libraries like Redux and Zustand. It’s even better if they understand React’s render behavior and can optimize performance with memorization and lazy loading. Like every framework, API integration and authentication flows are a must.
Knowing that tech giants built their empires on React, it’s easy to see why good React developers are in high demand.
Next.js developers: Next.js is built on React and adds critical features like server-side rendering, static site generation, and edge functions. Next.js developers should be comfortable with routing conventions, dynamic rendering strategies, and performance optimization techniques like image compression and incremental static regeneration. For full stack capabilities, they should also have a firm handle on middleware and API routes.
As a React framework, Next.js is excellent for improved site performance and SEO. Some popular applications that use Next.js include:
Thanks to optimized performance, it makes sense that streaming services and generative AI apps would use Next.js. However, a variety of industries use this framework.
Vue developers: Using component-based architecture, Vue makes it easy to create reusable, self-contained components. The result is less redundancy and faster project timelines. A Vue developer should know Vue Router, Vuex, Composition API, and Options API. It’s critical that your developer maintain clean component structures, slot usage, and reactive data handling.
Thanks to its simplicity, scalability, and flexibility, Vue powers the following popular applications:
The learning curve for Vue is lower than other frameworks, so it’s simpler than other options. However, it’s perfect for projects that don’t have complex requirements.
Angular developers: The best Angular developers will have experience with TypeScript, Angular CLI, RxJS, and services architecture. It’s crucial for them to understand component-driven design, dependency injection, and observable streams.
Maintained by Google, Angular builds dynamic single-page applications with a strong emphasis on testability and performance. Notable Angular apps include:
Angular’s structure and built-in tooling make it ideal for large enterprise applications. It’s a bit mire complex than other frameworks, but the result is a consistent, scalable, easy-to-maintain project.
3. Deep knowledge of DOM APIs
Good JavaScript developers should be able to write code that manipulates the DOM without relying on frameworks. They should also have experience with Fetch, Local Storage, and WebSockets. These particular APIs are fundamental to web apps and are essential for browser integrations.
Testing and debugging expertise
An application isn’t complete until it’s tested and shown to be reliable. A good developer will know how to use relevant testing tools like Mocha, Cypress, Jest, and React Testing Library. They’ll also be able to use browser dev tools effectively and write useful logs.
They use version control and collaborate
You want a JavaScript developer who collaborates well and uses version control. They should know how to branch, merge, rebase, resolve conflicts, and write meaningful commit messages. You’re in good hands if your developer has used GitHub Actions, GitLab CI, or similar automated testing/deployment pipelines.
Their code is easily maintained
Great JavaScript code is designed to evolve. Developers should be able to break UIs into reusable components and structure applications modularly. Their code should be simple and readable while avoiding repetition.
They have good communication and problem-solving skills
Coding is about more than just writing applications. Technical skills are great, but your ideal developer should be able to work well with others and troubleshoot quickly. A good developer can explain their code decisions to non-technical stakeholders and is up-to-date with current best practices.
They have full-stack experience for full-stack roles
If you’re hiring for a full-stack role, make sure your developer has the back-end knowledge to get the job done. For instance, they’ll need the ability to work with Express, RESTful APIs, GraphQL, MongoDB, and PostgreSQL.
They’re focused on the user experience
A great coder prioritizes performance. Using lazy loading, code splitting, and caching shows that a developer is thinking about the user experience. They should know how to, and have a system in place for measuring and improving app performance with pro tools like Lighthouse or Chrome DevTools.
They have a solid portfolio with code samples
Resumes are great, but you need solid proof of skills. That’s where live projects come in. Look for, or request access to active repos with well-documented code, readmes, and commit histories. They should have at least some public work, even if it was just created for their resume.
11 JavaScript developer red flags
Beware of the following red flags when hiring JavaScript developers:
A long list of frameworks
While it’s nice to find developers who have extensive knowledge, be wary of developers with a long list of frameworks on their resume, but can’t explain how they’re best used.
Over-reliance on jQuery
jQuery isn’t necessarily bad, but it’s outdated for a lot of today’s applications. When a developer lists jQuery as a primary skill, it’s a sign that their skillset might be outdated.
Not writing tests
If a JavaScript developer says they don’t write tests, that’s a liability. Hiring a developer that doesn’t prioritize testing and debugging is risky. You might end up with buggy applications and code that can’t be maintained.
They’re a lone wolf
There’s nothing wrong with working on projects solo, but if you’re planning on scaling development and need someone to work with a team, you need a developer with experience in a collaborative environment. No matter how skilled a JavaScript developer is, if they don’t know how to work on a team, it could spell disaster for your project.
A messy GitHub
Make it a point to check out a potential developer’s GitHub. If it’s a mess of global variables and long, unstructured functions, that’s a big red flag.
Flawed backend logic
When a developer’s API handling is clunky and doesn’t handle errors gracefully, that’s a red flag you don’t want to ignore.
No focus on performance
If a JavaScript developer can’t show you how they’ve improved an application’s performance, they’re probably not thinking about the user experience.
No public work available
Hiring a developer without seeing what they can do is a huge risk. Not everyone can share their client projects, but if that’s the case, a good developer will create at least something to demonstrate their abilities. If they can’t show you open-source tools they’ve built, blog posts they’ve written, or even just code samples, they could be a risk.
Poor communication skills
Even highly technical roles require clear communication. If a developer can’t give or receive feedback, or document code effectively, collaboration will suffer on larger teams.
Code review avoidance
If a developer resists collaborative practices like code reviews or pair programing, that might be a sign of a poor team player. These processes are essential for maintaining quality.
They ignore security and/or accessibility
Developers need to implement basic web accessibility (like semantic HTML, ARIA, and keyboard navigation) to meet Web Content Accessibility Guidelines. They also need to consider common security issues like XSS, CORS, and sanitizing inputs. If they lack awareness or concern for security or accessibility, they are a liability.
How to interview a JavaScript developer and ask the right questions
Confirming basic development knowledge and skills is the easy part. You’ll also want to assess how a developer thinks, codes, and communicates. A strong interview process will combine technical screening with an assessment for how they’ll fit into your team. You want to hire someone who meets your requirements, has the right skills, and is a match for your company culture.
Start with a conversation rather than a quiz. Ease into your interview with open-ended questions designed to reveal their thought process and how they approach challenges. Ask questions like, “Tell me about a project you’re proud of. What role did you play?”
Look for ownership, problem-solving, collaboration, and how they describe their impact on the project.
Next, get into technical knowledge. Ask questions like, “Can you explain how closures work?” or “What’s the difference between == and ===?”
Look for clarity and correctness. The ability to explain a concept is a sign of true understanding.
Next, provide practical code challenges. Give them a reasonable real-world problem to solve, like a web app with a performance issue, and ask them how they’d debug it.
Finally, test their ability to collaborate and communicate. Use roleplaying or situational questions to see how they’d handle team dynamics. For instance, ask how they give feedback in a code review, or what they’d do if a teammate pushed code that broke the build. What you’re looking for here is emotional intelligence, accountability, and the ability to be assertive while remaining respectful.
Remember to leave room for questions. A great developer should also evaluate you and your projects to see if you’re a fit. Pay attention to what they ask. If they only seem concerned about their pay, they might not engage deeply with your projects, and that will negatively impact your team.
A successful interview should leave you with a clear picture of a potential developer’s technical ability, problem-solving style, and how well they’ll fit in with your team.
Hire for skill, mindset, and fit
Hiring a JavaScript developer requires more than just checking off a list of skills. You need someone who can grow with your team, write maintainable code, and problem-solve on the fly. When you know what to look for – and what to avoid – you’ll have an easier time finding a proficient developer who will seamlessly integrate into your existing team and collaborate well.
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