Senior Frontend Software Engineer

Senior-level frontend software engineer with 6+ years of experience building production web applications and JavaScript single-page applications. They should be proficient in React, JavaScript, HTML5, CSS3, jQuery, Redux, CSS preprocessors, responsive design, Git, databases, and cross-browser development. They should be familiar with building user interfaces, managing application state, handling asynchronous requests and REST APIs, implementing partial page updates, and collaborating with designers, machine learning engineers, and backend developers.

1. How would you structure a scalable React single-page application with multiple feature areas?

I would organize the application by features, separating components, state logic, API services, and shared utilities. I would use reusable presentational components, container or hook-based logic, clear routing boundaries, and consistent conventions for error handling and data loading.

2. How do you decide what belongs in Redux versus local React state?

I use local state for component-specific concerns such as form inputs or toggles, and Redux for shared, persistent, or cross-route state such as authenticated users, entities, and application-wide status. State should be normalized where appropriate, with actions and reducers designed to keep updates predictable.

3. How would you handle asynchronous REST API requests in a React application?

I would isolate API calls in a service layer and manage loading, success, empty, and error states explicitly. Depending on the project, I would use Redux middleware or a data-fetching library, while also handling cancellation, retries, request deduplication, and stale responses.

4. What techniques do you use to optimize rendering performance in a large React application?

I profile first, then reduce unnecessary renders using stable props, memoization, selector optimization, and component boundaries. I also use code splitting, lazy loading, list virtualization, efficient event handling, and minimized bundle sizes when appropriate.

5. How would you implement responsive behavior using HTML5, CSS3, and SASS or LESS?

I would use semantic HTML, mobile-first CSS, flexible layouts with Flexbox or Grid, and breakpoint-based media queries. SASS or LESS can provide variables, mixins, nesting, and shared design tokens, but the compiled CSS should remain maintainable and avoid excessive specificity.

6. How do you ensure cross-browser compatibility for a modern JavaScript application?

I define supported browsers, use feature detection and appropriate polyfills, and verify behavior through automated and manual testing. I also account for differences in CSS support, event behavior, layout rendering, and JavaScript APIs rather than relying only on a single browser.

7. How would you design partial page updates without causing inconsistent application state?

I would update state through a single predictable flow, using normalized entities and immutable updates where applicable. API responses should be reconciled carefully with existing state, while optimistic updates require rollback logic if the server request fails.

8. What is your approach to designing reusable JavaScript components and modules?

I define clear interfaces, keep components focused on one responsibility, and avoid coupling them to specific API or business logic details. Shared behavior should be extracted into hooks, utilities, or services while preserving flexibility through composition and well-defined properties.

9. How do frontend data structures affect the performance and maintainability of an application?

Choosing arrays, maps, sets, or normalized object structures affects lookup complexity, update cost, and rendering behavior. For frequently accessed entities, keyed structures can provide efficient updates and avoid duplicated data, while selectors can expose convenient views to components.

10. How do you use Git effectively when collaborating with frontend, backend, design, and machine learning teams?

I use focused branches, descriptive commits, pull requests, and frequent synchronization with the main branch. I resolve conflicts carefully, keep commits reviewable, document API or UI contract changes, and use automated checks such as linting, tests, and builds before merging.

Entefy is a mission-driven technology company building intelligent digital interaction through beautiful, powerful web experiences. As a Senior Frontend Software Engineer, you’ll develop scalable features across web application layers while collaborating with software, machine learning, and visual design teams. Work remotely with a stack including JavaScript, ReactJS, Redux, HTML5, CSS3, jQuery, LESS/SASS, REST APIs, AJAX, and Git; salary details are not disclosed. Apply to solve ambitious problems, shape next-generation products, and work alongside a highly talented, collaborative team.