Hiring guide
How to Hire a JavaScript Developer
Hire a JavaScript developer who knows core JavaScript as well as your framework: async and DOM skills, a bug-fix work sample, red flags and onboarding.
The short answer
Hiring a JavaScript Developer comes down to verifying core language: closures, scope, prototypes, this binding, modules and equality rules, asynchronous code: promises, async/await, the event loop, cancellation and error handling and typescript if your codebase uses it, with sensible types rather than any everywhere before you commit interview time. The process below runs 5 stages, screens on evidence rather than résumé claims, and scores every candidate against the same criteria.
- Watch for: Cannot explain what happens when a promise rejects with no handler
- Watch for: Adds a new npm package for every small task without checking size or maintenance
- Score on: Correct handling of asynchronous behaviour and errors
- Score on: Understanding of the language beyond the framework
Paste your JavaScript Developer job description; Cohesyve finds, contacts and tests candidates on the real work and ranks them. Ten candidates free, no card.
Applying for a role like this? Practise the assessment free →To hire a JavaScript developer well, decide whether you need browser work, Node.js back-end work or both, and which framework, if any, you use. Many candidates know a framework's patterns without understanding the language beneath it, which shows when something breaks. Test core JavaScript and asynchronous behaviour as well as the framework.
Why this role matters
JavaScript runs your user interface and often your server code too. Weak understanding of asynchronous code produces race conditions and unhandled errors, careless bundles slow your pages, and poor handling of user input creates security problems such as cross-site scripting. A strong JavaScript developer writes code that stays fast and predictable as features pile up, and picks dependencies carefully.
Where to find candidates
- GitHub and npm, looking at maintainers and contributors of packages similar to what you build
- Local JavaScript, React, Vue and Node.js meetups and their speakers
- Holders of OpenJS Foundation Node.js certifications (JSNAD and JSNSD) for Node.js-heavy roles, as one signal among others
- Hacker News "Who is hiring?" threads and developer communities such as DEV
- Front-end and JavaScript newsletters' job sections and community Discord servers
- Referrals from your engineers who have reviewed the candidate's pull requests in open source
Skills to look for
Red flags
- Cannot explain what happens when a promise rejects with no handler
- Adds a new npm package for every small task without checking size or maintenance
- Framework knowledge only, struggling to write plain JavaScript or handle DOM events directly
- Ignores TypeScript errors by casting to any
- No awareness of accessibility in interactive components
- Cannot use browser dev tools to profile or debug network requests
The interview process
- 1
Portfolio and code review
Review a repository or pull requests they wrote. Ask why they structured state the way they did and how they handled errors in async code.
- 2
Core JavaScript conversation
Talk through short snippets: the output order of mixed setTimeout and promise code, a closure in a loop, or a this binding bug. Focus on how clearly they explain the behaviour.
- 3
Bug-fix and feature work sample
Give a small app in your framework with a real-looking bug, such as a search box that shows stale results when requests return out of order, plus a small feature to add. A job simulation of the real work is one option for this step. Judge how they find the cause, the fix, tests and accessibility.
- 4
Review discussion
Ask them to walk through their changes and then review a short pull request from your team. Look for useful, specific comments.
- 5
Team interview and references
Meet the designer or product manager they would work with. Ask references about code quality and how they pick libraries.
Cohesyve
Start the JavaScript Developer interviews from a ranked shortlist
Cohesyve takes your JavaScript Developer job description, finds and contacts candidates and tests each one on an AI job simulation of the job, so the stages above start with people who have already done the work. Ten candidates free, no card.
How to evaluate
- Correct handling of asynchronous behaviour and errors
- Understanding of the language beyond the framework
- Accessible, keyboard-usable interactive components
- Thoughtful dependency choices and attention to bundle size
- Tests that cover the bug they fixed
- Clear explanation of their debugging process
Onboarding
- 1Document Node.js version, package manager, lint rules and TypeScript settings
- 2Explain your rules for adding dependencies and who approves them
- 3Start with a bug fix in a well-tested area so they learn the codebase safely
- 4Share your performance and accessibility checks and where they run in CI
- 5Pair with a senior developer on their first larger feature
Common questions
Should I hire a JavaScript developer or a React developer?
If your product is built in React, hire someone strong in React, but test core JavaScript as well. Framework skills date quickly, while language understanding carries over.
Do I need TypeScript experience?
If your codebase uses TypeScript, yes for most roles. A strong JavaScript developer can learn it, but expect early pull requests to need type guidance.
How do I test Node.js back-end JavaScript skills?
Use a small API task with input validation, an async call to a database or external service, error handling and a test. Watch for unhandled rejections and blocking work on the event loop.
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