Interview Experience with EY as a React.js Frontend Engineer

Overview

This article details the interview process for a React.js Frontend Engineer position at Ernst & Young (EY). The interview assessed the candidate's proficiency in JavaScript, React.js, and general frontend development principles. The process aimed to evaluate the candidate's technical foundation, problem-solving capabilities, and understanding of best practices.

Interview Rounds

The interview process consisted of two technical rounds.

Technical Round 1: The Foundation Test

This virtual round focused on core JavaScript and React.js knowledge. The interviewer posed a combination of theoretical and coding questions to gauge the candidate's comprehension.

JavaScript Fundamentals

• The candidate was asked to explain the differences between variable declarations (var, let, const) and function declarations (function declarations, function expressions, and arrow functions).
• The candidate explained hoisting, bindings, and closures in JavaScript, providing examples of how var and function declarations are hoisted. They discussed lexical scope and closures in depth.

React.js Essentials

• The candidate described how the React Virtual DOM enhances performance, explaining the diffing algorithm and reconciliation process and how React efficiently updates only the changed parts of the DOM.
• The candidate highlighted the advantages of using hooks and custom hooks in React, including cleaner code, stateful logic reuse, and performance improvements through useMemo and useCallback.
• The candidate discussed the differences between functional and class components in React, addressing lifecycle methods vs. hooks, readability, performance improvements, and why React favors functional components.
• The candidate explained state management patterns, including useState, useReducer, Context API, and external solutions like Redux or Zustand.

Optimization & Best Practices

• The candidate explained how keys help React identify elements efficiently and prevent unnecessary re-renders.
• The candidate outlined the lifecycle phases (Mounting, Updating, Unmounting) and their equivalent hooks (useEffect, useLayoutEffect).
• The candidate discussed techniques like memoization, lazy loading, code splitting, and avoiding unnecessary renders with React.memo.
• The candidate demonstrated how useMemo optimizes computations, useCallback memoizes functions, useRef preserves values across renders, and useReducer handles complex state logic.
• The candidate discussed global state management, when to use Context API over Redux, and how it reduces prop drilling.
• The candidate discussed ARIA attributes, semantic HTML, keyboard navigation, and color contrast considerations.

JavaScript Coding Problems

The candidate solved coding challenges involving object manipulation, array transformations, and higher-order functions like map, filter, and reduce.

Technical Round 2: The On-Site Challenge

This round involved coding challenges, advanced React topics, and frontend performance optimizations.

Coding & Problem-Solving

• The candidate tackled more complex coding challenges, including recursion, asynchronous programming, and deep object cloning.
• The candidate built a React component with proper state management, context integration, and performance optimizations.

HTML & CSS

• The candidate discussed specificity, flexbox vs. grid, animations, BEM methodology, and performance optimizations like will-change.
• The candidate covered semantic HTML, lazy loading, preloading, and best practices for SEO.

Performance, Security & Tooling

• The candidate discussed how to improve application performance, avoid memory leaks, and enhance UX with efficient state management.
• The candidate engaged in a deep dive into event delegation, reconciliation process, and browser rendering optimizations.
• The candidate explored common security risks like XSS, CSRF, and best practices for securing React applications.
• The candidate discussed bundling, tree shaking, code splitting, and dependency management with NPM/Yarn.

Key Takeaways

• Master the Fundamentals: Solid JavaScript knowledge is essential for any frontend role.
• Deep Dive into React: Understanding React's internals is crucial, not just its usage.
• Performance & Optimization Matter: Employers highly value efficiency in code and UI.
• Security & Best Practices: Secure coding is just as crucial as writing functional code.
• Systematic Problem-Solving: Breaking down problems and approaching them logically is critical.