Instana India Frontend Engineer Interview: Rounds, Questions and Preparation

What the job involves

Frontend Engineers at global product companies build and maintain the user-facing parts of web applications, often working on complex dashboards and data visualisation. Day to day, they write JavaScript or TypeScript, use frameworks like React or Vue, collaborate with designers and backend engineers, and ensure performance and accessibility across browsers. In fast-growing product teams, they also debug production issues, write tests, and contribute to component libraries.

Role and technical knowledge

1. 1

   Explain the event loop in JavaScript and how it handles asynchronous callbacks.

   Cover call stack, task queue, microtask queue, and how promises differ from setTimeout. Use a simple example to show order of execution.

2. 2

   What is the difference between state and props in React, and when would you use each?

   State is mutable and managed within a component; props are read-only and passed from parent. Mention lifting state up and controlled components.

3. 3

   How do you optimise a slow-loading web page?

   Discuss code splitting, lazy loading, image optimisation, caching, reducing bundle size, and using performance tools like Lighthouse.

4. 4

   What are semantic HTML elements and why are they important?

   Explain elements like header, nav, main, article. Mention accessibility, SEO, and maintainability benefits.

Practical scenarios

1. 5

   You need to build a dashboard that displays real-time metrics updating every second. How would you approach it?

   Discuss WebSockets or polling, state management, efficient re-renders, and using virtualisation for large lists.

2. 6

   A component works in Chrome but breaks in Safari. How do you debug and fix it?

   Check browser compatibility, use caniuse, polyfills, and feature detection. Mention testing on multiple browsers and using developer tools.

3. 7

   How would you make a complex form accessible to screen reader users?

   Cover labels, ARIA attributes, keyboard navigation, focus management, and error announcements.

4. 8

   You are asked to add a new feature to an existing codebase with no tests. What do you do?

   Suggest writing tests for the new feature first, then gradually adding tests around the changed area. Mention communication with the team.

Behavioural and HR questions

1. 9

   Tell me about a time you had to learn a new frontend framework or tool quickly.

   Use STAR method. Highlight how you approached learning, resources used, and the outcome.

2. 10

   Describe a situation where you disagreed with a teammate on a technical decision.

   Show respect, data-driven discussion, and willingness to compromise or escalate constructively.

3. 11

   Why do you want to work as a frontend engineer at a product company like ours?

   Connect your interest in building user-facing products, mention the company's domain or tech stack, and show enthusiasm for learning.

4. 12

   How do you handle tight deadlines when you have multiple tasks?

   Talk about prioritisation, communication with stakeholders, breaking work into smaller chunks, and asking for help when needed.

Problem solving and coding approach

1. 13

   Given an array of objects representing user data, write a function to group users by their city.

   Use reduce or a simple loop. Explain time complexity and handle edge cases like missing city.

2. 14

   How would you implement a debounce function in JavaScript?

   Explain the concept, use setTimeout and clearTimeout, and show a simple implementation with arguments and context.

3. 15

   Write a function to flatten a nested array without using Array.flat().

   Use recursion or reduce. Discuss handling different depths and non-array elements.

4. 16

   Explain how you would test a React component that fetches data from an API.

   Mention mocking fetch or axios, using React Testing Library, waiting for async updates, and asserting on rendered output.