AB Tasty 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 with frameworks like React or Vue and integrating with APIs and A/B testing tools. Day to day they write clean, reusable components, collaborate with designers and backend engineers, and optimise performance and accessibility. In fast-growing product teams, they also contribute to experimentation, analytics dashboards, and customer-facing features.

Role and Technical Knowledge

1. 1

   What is the difference between var, let, and const in JavaScript, and how does hoisting work?

   Explain block scoping, temporal dead zone, and how var is function-scoped and hoisted with undefined. Give a small code example.

2. 2

   How does the virtual DOM work in React, and why does it improve performance?

   Cover diffing algorithm, reconciliation, and batched updates. Mention that it minimises direct DOM manipulation but is not always faster than manual DOM.

3. 3

   Explain how you would make a web page responsive using CSS.

   Mention media queries, flexbox, grid, relative units (rem, vw), and mobile-first approach. Give a concrete example of a layout that changes at breakpoints.

4. 4

   What are the different ways to manage state in a React application, and when would you choose each?

   Compare local state, Context API, Redux, and server state (React Query). Discuss trade-offs in complexity, performance, and team size.

Practical Scenarios

1. 5

   You need to build a feature that shows a list of experiments with a toggle to enable or disable each. How would you structure the components and handle API calls?

   Describe a parent component fetching data, child components for each item, optimistic UI updates, and error handling. Mention loading and empty states.

2. 6

   A page is loading slowly because of a large JavaScript bundle. How would you debug and improve it?

   Talk about using Lighthouse, code splitting, lazy loading, tree shaking, and caching. Suggest measuring before and after with performance metrics.

3. 7

   How would you ensure your frontend code is accessible to users with disabilities?

   Mention semantic HTML, ARIA roles, keyboard navigation, colour contrast, and testing with screen readers. Give an example of fixing a common issue like missing alt text.

4. 8

   You are integrating an A/B testing tool that injects a script on the page. How would you avoid it breaking your app or slowing it down?

   Discuss loading scripts asynchronously, feature flags, error boundaries, and testing in staging. Mention isolating third-party code and monitoring performance.

Behavioural and HR

1. 9

   Tell me about a time you had to learn a new frontend technology quickly for a project.

   Use STAR method: describe the project, the technology, how you learned it (docs, tutorials, pair programming), and the outcome. Show curiosity and self-learning.

2. 10

   Describe a situation where you disagreed with a teammate about a technical approach. How did you handle it?

   Focus on listening, discussing trade-offs with data, and reaching a consensus. Show you can separate ego from the best solution.

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 features with the company's product (e.g., experimentation, analytics). Mention specific technologies or values from the job description.

4. 12

   How do you prioritise tasks when you have multiple deadlines, such as a bug fix and a new feature?

   Explain assessing impact and urgency, communicating with your manager, and using tools like a task board. Give an example of a time you managed competing priorities.

Coding and Problem Solving

1. 13

   Write a function that takes an array of objects and returns a new array with only the items that match a given property value.

   Use filter and explain time complexity. Write clean, readable code with descriptive variable names.

2. 14

   Implement a debounce function in JavaScript.

   Cover closure, setTimeout, clearTimeout, and use cases like search input. Explain how it differs from throttle.

3. 15

   Given a string, write a function to check if it is a palindrome, ignoring case and non-alphanumeric characters.

   Normalise the string, use two pointers or reverse comparison. Discuss edge cases like empty string and unicode.

4. 16

   How would you flatten a nested array in JavaScript without using flat()?

   Use recursion or reduce. Explain how you handle different depths and avoid stack overflow for very deep arrays.