App Design Questions (Machine Coding) in Front-End Interviews (2025 Guide)
If you’re preparing for frontend interviews, you’ve likely already encountered questions about app design. But what are they exactly? MDN’s guide to DOM scripting covers the vanilla JavaScript side.
App design questions are practical questions that ask you to build a small application. That could mean creating a to-do list, a photo gallery, a tic-tac-toe game, or an autocomplete search box. These aren’t theoretical; they test your real-world engineering ability to build, organize, and scale UI applications. You will most likely be asked to make these using React or vanilla JavaScript.
How to Prepare for App Design Rounds
The most significant piece of advice: don’t just focus on building the feature. You also need to demonstrate that you can scale it effectively.
Things to think about:
- Component design: How will you break your UI into components?
- State management: Are you using
useState?useContext?Redux? - Data flow: Can your app handle updates and props cleanly without unnecessary re-renders?
Yes, even in a 45-minute interview, it might make sense to use Redux depending on the problem. In most cases, you’ll use useState and then discuss how the app could evolve using useContext Or Redux as it grows in complexity. Ensure you can clearly explain the advantages and disadvantages of each approach.
I recommend using the MVVM (Model-View-ViewModel) design pattern for structuring your React components. I wrote an in-depth article about it here: MVVM Pattern in React
Performance Tips to Call Out
Interviewers love hearing you think about performance, especially if you mention it before they do.
- Caching: LocalStorage, SessionStorage, Cookies, or IndexedDB (talk about them even if you don’t have time to implement)
- Debouncing: If you’re building an autocomplete, debounce your API calls using Lodash or a custom debounce utility
- Infinite scrolling: Use
IntersectionObserverto detect when the user hits the bottom of the list - Pagination: Bonus points if you discuss cursor-based pagination vs. page-based pagination
Even if you can’t implement all of this in the interview, talking about these patterns shows senior-level thinking.
Expect to Fetch & Render
Many app design questions involve fetching data from an API, rendering it in the DOM, and applying styling, including hover effects or transitions.
If you’re building something like a list or a grid, discuss:
- Virtualized lists (
react-window,react-virtualized) for performance - When and how you’d trigger data loading
- How do you organize the UI for reusability
Recommended App Design Practice Questions
FrontendLead offers a growing list of app design questions you can practice here: Practice App Design Questions
Some great ones to start with:
- Build a to-do list (great for covering full CRUD)
- Build a photo gallery with fetched images
- Build an image slider
- Build a masonry layout
- Build a chat app UI
- Build a search bar with debounce
- Build a mini Airbnb-style listing UI
The point is to build lots of small UIs and optimize them as you go.
Below is a table showcasing typical app design questions you might encounter, with examples in both React and Vanilla JavaScript:
| App Type | Description | React Example | Vanilla JS Example |
|---|---|---|---|
| To-do List | Create an app to manage daily tasks | Use state to manage list items | Manipulate the DOM to add/remove tasks |
| Photo Gallery | Develop a grid-based photo display app | Use components for gallery items | Use CSS Grid for layout |
| Image Slider | Build a carousel for navigating through images | Implement with React state for the active slide | Use timers and DOM manipulation |
| Masonry Layout | Create a Pinterest-like column-based layout | Use CSS Modules for styling | Apply column-width CSS dynamically |
| Tic Tac Toe | Design a game with a minimal user interface | Use React state for storing the game board | Track clicks and check for win conditions |
| Small Game | Develop a simple interactive game like Snake | Leverage React effects for game logic | Use Canvas API for rendering |
What About React vs. Vanilla JavaScript?
Most companies will expect you to use React. However, some platforms (like Google) may require you to use only HTML, CSS, and JavaScript. So it’s worth being ready for both.
That said, Google typically doesn’t ask full-blown app design questions. They may instead request minor variations, such as adding an accessible checkbox, a toggle button, or a dropdown.
Final Thoughts
If you’re serious about front-end interviews, app design questions are a must-practice category. They reflect the kind of work you’ll be doing, and they’re the most fun to solve, too.
Try building 5–10 small apps before your interviews. Learn to structure your code, manage state, and discuss trade-offs as you create. That’s how you’ll stand out.
You can get started with app design questions here: Start Practicing