How My Friend Cracked a 25+ LPA Frontend Engineer Role at Persistent Systems

Overview

Landing a high-paying Frontend Engineer position requires a robust understanding of JavaScript, scalable architecture, and effective decision-making. Persistent Systems, like many leading tech companies, emphasizes these skills during their interview process.

This document details the interview experience of a candidate who received a 25+ LPA offer for a Frontend Engineer role at Persistent Systems, offering insights into the questions asked and the skills evaluated.

Interview Rounds

The interview process consisted of three rounds: a technical interview focusing on JavaScript and React, an advanced technical round emphasizing system design for the frontend, and a managerial/behavioral interview.

🧪 Round 1 — Technical Interview (JavaScript + React)

This round assessed the candidate's proficiency in core JavaScript concepts, React hooks, performance optimization techniques, and the ability to build reusable components.

Key Questions Asked:

1. Explain the Event Loop and how asynchronous tasks execute in JavaScript.
   • Topics expected: Call stack, microtasks, macrotasks, priorities.
2. Implement a custom React Hook for debouncing input value.
   • Tested: useEffect, cleanup functions, controlled input logic.
3. Build a reusable Dropdown component with:
   • Search support
   • Multi-select capability
   • Keyboard accessibility (bonus)
4. How would you optimize React rendering in a list with 10,000+ rows?
   • Expected approaches: Virtualization (React Window / React Virtual), Memoization, useCallback, React.memo, selective re-renders.
5. Difference between Controlled vs. Uncontrolled components with examples.

🧱 Round 2 — Advanced Technical / System Design for Frontend

This round evaluated the candidate's understanding of scalable React architectures, Next.js internals, performance optimization strategies, and cross-team collaboration skills.

Key Questions Asked:

1. How would you design a scalable React dashboard with 100+ pages?
   • Expected topics: Folder structure, module separation, routing strategy, micro-frontend possibilities.
2. Explain Code Splitting & Lazy Loading and how they improve performance.
3. How do you handle API rate limits gracefully on the frontend?
   • Suggested topics: retries, exponential backoff, caching, debouncing, queueing.
4. What is Hydration in Next.js? When does it cause UI mismatches?
5. How to build a shared component library used by multiple teams?
   • Monorepo, Storybook, versioning, semantic release, design tokens.
6. Explain CSR vs SSR vs SSG. When would you use each?
7. Design frontend architecture to handle 1M+ daily active users.
   • Expect discussion on: CDN caching, Perf budgets, Edge rendering, Lazy loading & prefetching, Analytics & monitoring.

👥 Round 3 — Managerial / Behavioral Interview

This round assessed the candidate's ownership, communication, leadership qualities, and problem-solving abilities.

Key Questions Asked:

1. Tell me about a time a critical production bug broke the UI. How did you handle it?
   • Look for: RCA, rollback, communication, monitoring.
2. How do you balance technical debt vs. new feature delivery?
3. Describe a conflict with a designer/backend team and how you resolved it.
4. How do you explain complex technical decisions to non-technical stakeholders?

Key Takeaways

To succeed in Frontend Engineer roles at companies like Persistent Systems, candidates should focus on the following areas:

• Technical Skills:
  • Deep JavaScript: event loop, promises, generators, proxies
  • React: performance, custom hooks, SSR/CSR/SSG, Next.js hydration
  • Component architecture & design systems
  • Web performance optimization & caching
  • API handling, rate-limiting strategies, error boundaries
• System Design for Frontend:
  • Micro frontends
  • Module federation
  • CDN, caching, edge rendering
  • Observability and monitoring
• Behavioral Preparation:
  • STAR method for structured answers
  • Conflict resolution stories
  • Production incident handling examples