Navigating Frontend System Design Interviews with the CCDAO Framework
A simple yet powerful tool that helps you structure your answers and stand out in system design interviews.
System Design interviews are challenging, even for experienced developers. Many front-end engineers are deeply immersed in delivering features for a single product, which doesn’t always translate into the broad, architectural thinking that system design questions demand. While industry experience provides some advantages—exposure to various software components, from UI to DevOps—success in a system design interview often hinges on adopting the right mindset and demonstrating key design principles.
In reality, not every company operates at the scale of a Meta or Google. This means that a lot of developers simply haven’t encountered massive scalability issues in their day jobs. Even if you’ve worked for a tech giant, you may only see a slice of the entire ecosystem—for instance, contributing to Facebook’s codebase doesn’t give you automatic insight into the architecture of Instagram. Real-world experience is valuable, but it’s often narrow in scope.
So, how do you effectively prepare for a frontend system design interview when you’re unsure where to begin? That’s exactly what this newsletter series is about. My goal is to help you structure your knowledge so you can develop a complete mental map of frontend architecture. This will not only enhance your ability to tackle new challenges but also help you communicate effectively during interviews.
Frameworks can act as roadmaps, ensuring you cover essential topics that interviewers care about—making it clearer that you and the interviewer speak the same technical language. Of course, interviewer styles vary, and there are factors beyond your control, but you can control how well you structure and deliver your thoughts.
Let’s dive into the CCDAO framework—five essential steps to guide you through a frontend system design interview. Memorizing this acronym will help you remain systematic and avoid missing important considerations.
The CCDAO Framework
The CCDAO stands for Collect information, Component Structure, Data Modelling, API Design and Optimisation Considerations, let’s break it down and see the simple framework can help you to organise your thoughts during the interview.
Collect Information
Core Functionality: Begin by clarifying the main features, user flows, and critical requirements. This might include navigation structure, data inputs, and key interactions.
Cross-Functional Requirements: Ascertain performance goals, security considerations (e.g., XSS prevention, CSRF tokens), accessibility standards (WCAG compliance), and user environment (are users on mobile devices with spotty networks?). Knowing these constraints up front shapes how you’ll architect the frontend.
Component Structure (Mockup)
UI Breakdown: Sketch a basic mockup or wireframe if none is provided. Identify logical React/Vue/Angular components, how they interact, and where to manage state (e.g., local component state vs. a global store).
Reusability & Modularity: Decide which components can be reused across the application and factor in a design system if available. For large-scale apps, consider whether a micro-frontend approach is beneficial.
Data Modeling
Frontend Data Structure: Determine how data is fetched, stored, and updated within the client. For example, using normalized data in a Redux store vs. a more denormalized approach in React Query or SWR.
Offline or Partial Connectivity: If users may lose connectivity, discuss local caching (e.g., IndexedDB, service workers) or progressive web app (PWA) features.
Pagination & Large Datasets: Decide when and how to paginate or lazy-load data to keep the UI performant and responsive.
API Design
REST vs. GraphQL: Clarify how the frontend communicates with the backend. For instance, GraphQL might be beneficial when your UI needs flexibility in querying data.
Real-Time Updates: If real-time features are required (e.g., chat or live dashboards), consider WebSockets, Server-Sent Events (SSE), or libraries like Socket.io.
Security: Discuss handling of JSON Web Tokens (JWT), OAuth flows, and how you’ll protect client-side code and data from malicious inputs (CORS, content security policies, etc.).
Optimization Strategies
Performance Considerations
Code Splitting & Lazy Loading: Using dynamic imports or route-based splitting to reduce your initial bundle size.
Server-Side Rendering (SSR): Tools like Next.js or Nuxt can improve SEO and reduce time-to-interactive.
Caching: Both client-side (Apollo Client cache, Redux) and server-level caching (CDN, edge caching) can drastically improve load times.
Responsive & Fast UIs: Understand the critical rendering path, measure Web Vitals (LCP, CLS, FID), and optimize images and fonts.
Beyond the Happy Path
Error Handling: Use error boundaries (in React) or global error handlers for unexpected client-side crashes.
Fallback Mechanisms: Graceful degradation if the network is slow or unavailable. Skeleton screens, partial loading states, or local data storage can keep the app usable.
User Experience (UX)
Internationalization (i18n): Plan for multiple languages, time zones, and date formats.
Accessibility: Keyboard navigation, screen reader support, color contrast, and ARIA attributes.
Loading & Error States: Provide clear visual cues when fetching data or encountering errors to enhance user trust.
I have made a video on the topic too, if you prefer watching videos you can find it in my YouTube channel: https://www.youtube.com/@icodeit.juntao
Recommended Time Allocation for a 45-Minute Interview
Below is a sample way to structure your discussion in a typical 45-minute interview:
Collect Information: 5 minutes
Component Structure: 5 minutes
Data Modeling: 10 minutes
API Design: 10 minutes
Optimization Strategies: 15 minutes
The final Optimization segment often takes the most time because it touches on so many subtopics (performance, caching, error handling, etc.). If you have time, delving into accessibility, internationalization, and offline capabilities can really set you apart as a senior frontend candidate.
Why This Matters
A successful frontend system design interview isn’t just about reciting buzzwords; it’s about showing that you can think holistically. You’ll stand out if you can:
Adapt to the interviewer’s prompts and steer the conversation toward key frontend concerns (performance, UX, accessibility).
Demonstrate you understand typical trade-offs (e.g., REST vs. GraphQL, local state vs. global store) in a thoughtful manner.
Show an end-to-end user perspective, from fetching data to rendering polished, accessible UIs.
Remember, no article or newsletter can replace the insights gained from actual experience. However, by internalizing the CCDAO framework, you give yourself the best chance to cover essential design aspects smoothly and confidently in your next interview.
Have questions, or want more in-depth examples of how to apply CCDAO in real projects?
Reply to this newsletter or drop me a line on [your social platform of choice]. I’d love to hear your thoughts and experiences on tackling frontend system design interviews.
Stay curious, and best of luck with your interviewing journey!