American Express Tech India Frontend Engineer Interview: Rounds, Questions and Preparation

What the job involves

Frontend Engineers in global tech companies build and maintain the user-facing parts of web and mobile applications, turning design mockups into responsive, accessible, and performant interfaces. Day to day you write JavaScript/TypeScript, work with frameworks like React or Angular, integrate REST APIs, and collaborate with designers, backend engineers, and product managers. You also debug cross-browser issues, optimize load times, and write tests to ensure reliability.

Role and Technical Knowledge

1. 1

   Explain the difference between `var`, `let`, and `const` in JavaScript.

   Cover scoping (function vs block), hoisting, temporal dead zone, and reassignment rules. Give a small code example for each.

2. 2

   How does the virtual DOM work in React, and why is it useful?

   Describe how React creates a lightweight copy of the UI, diffs it on state changes, and updates only the real DOM. Mention performance benefits and reconciliation.

3. 3

   What are semantic HTML elements and why should you use them?

   Name examples like `<header>`, `<nav>`, `<main>`, `<article>`. Explain benefits for accessibility, SEO, and code readability.

4. 4

   Explain the CSS box model and how `box-sizing: border-box` changes it.

   Describe content, padding, border, margin. Clarify that border-box includes padding and border in the element's total width/height, making layout easier.

Practical Scenarios

1. 5

   A web page loads slowly because of large images and many JavaScript files. How would you improve performance?

   Suggest lazy loading, image compression, code splitting, minification, caching, and using a CDN. Mention measuring with Lighthouse first.

2. 6

   You need to fetch data from an API and display a list of transactions. How do you handle loading and error states?

   Use state for loading, error, and data. Show a spinner while loading, an error message with retry on failure, and render the list only when data arrives. Mention useEffect or similar.

3. 7

   How would you make a form accessible to screen readers?

   Use proper labels linked to inputs, ARIA attributes where needed, keyboard navigation, focus management, and error announcements. Avoid placeholder-only labels.

4. 8

   You are asked to build a responsive navigation bar that collapses into a hamburger menu on mobile. Walk through your approach.

   Describe using CSS media queries or a mobile-first approach, toggling a class with JavaScript, ensuring touch targets are large enough, and testing on multiple screen sizes.

Behavioural and HR

1. 9

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

   Use STAR format: situation, task, action, result. Highlight how you found resources, practiced, and applied it successfully.

2. 10

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

   Show respect, focus on data and user impact, and willingness to compromise or escalate constructively. End with a positive outcome.

3. 11

   Why do you want to work as a Frontend Engineer in a global tech company?

   Connect your interest in user experience, scale, and continuous learning to the company's products and engineering culture. Avoid generic answers.

4. 12

   How do you prioritize tasks when you have multiple deadlines?

   Mention assessing impact and urgency, communicating with stakeholders, using tools like Jira or Trello, and breaking work into smaller chunks.

Coding and Problem Solving

1. 13

   Write a function to debounce another function in JavaScript.

   Explain the use case (e.g., search input). Implement with setTimeout and clearTimeout, returning a closure that delays execution until after a pause.

2. 14

   Given an array of numbers, return the two numbers that add up to a target sum.

   Discuss brute force vs hash map approach. Code the O(n) solution using a map to store complements. Handle edge cases like no solution.

3. 15

   How would you reverse a linked list?

   Explain iterative approach with three pointers (prev, current, next). Walk through the loop and update pointers. Mention time O(n) and space O(1).

4. 16

   Implement a function that flattens a nested array without using `Array.prototype.flat`.

   Use recursion or reduce. Show how to check if an element is an array and concatenate results. Mention handling deep nesting.