Hire JavaScript Developers Across the Whole Stack

How to vet a JavaScript developer

JavaScript is easy to start and hard to master, so surface-level familiarity is common. Strong developers understand the event loop, asynchronous code with promises and async functions, closures, scope and how the browser renders a page. They can explain why a piece of code behaves unexpectedly rather than adding workarounds until it seems to work, and they read error messages and stack traces calmly.

Beyond the language, look at how candidates structure code: modules, naming, small functions and tests. Ask what they would change in a codebase they inherited, and how they handle older patterns such as jQuery or callbacks. Most professional JavaScript work now uses TypeScript as well, so comfort with types is increasingly expected even for roles described as JavaScript.

• Explains the event loop and asynchronous behavior clearly.
• Writes modular, readable code with tests.
• Understands browser rendering and performance basics.
• Comfortable with modern tooling such as Vite and ESLint.
• Can work with both modern frameworks and legacy code.
• Uses browser developer tools fluently for debugging.

Interview questions we use for JavaScript developers

We use practical questions that reveal understanding of the language and the browser. Candidates talk through real bugs they have fixed and write small snippets, and we pay attention to how they reason when they are unsure. We also ask how they keep code readable for teammates.

Good answers connect concepts to consequences: why a forgotten await caused a race condition, why a large bundle hurt mobile users or why a memory leak appeared in a long-lived page. Candidates who can explain these clearly usually write code that teammates can maintain without surprises.

• What is the output order of a snippet mixing setTimeout, promises and synchronous logs, and why?
• How would you debounce a search input, and when would you throttle instead?
• How do you find and fix a memory leak in a single-page application?
• What are the differences between var, let and const in practice?
• How would you migrate a jQuery-heavy page to a modern framework gradually?
• How do you handle errors in chains of asynchronous calls?

Onboarding a JavaScript developer in the first two weeks

Week one covers environment setup, code conventions and architecture. The developer runs the application locally, reads key modules and recent pull requests, and fixes small issues that touch different parts of the codebase. Pairing with an existing team member on one task shows how reviews, tests and deployments work in practice, which shortens the learning curve considerably. Questions are encouraged from day one.

In week two, the developer delivers a scoped feature with tests and takes part fully in planning and reviews. If the codebase is moving to TypeScript, they may also convert a module as a learning exercise. Our TypeScript vs JavaScript comparison explains why many teams make that move, and our TypeScript developers can lead larger migrations.