SoFi·Frontend Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say

Apr 2026

Summary

System design round at SoFi for a frontend engineer role, focused entirely on building a notification system in a SPA. No backend stuff, just the frontend layer, which was actually a nice constraint for once.

Questions Asked (1)

Design the frontend for an in-app notification system in a single-page application built on a shared component library. Cover the component API and props, the data model, state management, real-time updates, debouncing, and cross-tab sync. Frontend only.

System DesignTechnical Trade-offsData Modeling

Author's notes

This was the whole interview, one big question.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then walk through the design in layers: component API, data model, state management, real-time updates, debouncing, and cross-tab sync. Emphasize trade-offs and how the shared component library influences decisions, and finish with a brief summary of key choices.

Pro tip: Demonstrate awareness of the shared component library by discussing how to extend it without breaking other consumers, and mention accessibility (ARIA live regions) for notifications—this shows maturity beyond just technical implementation.

1. Clarify Requirements and Constraints

Ask questions to understand scale, notification types, real-time expectations, and cross-tab needs. Confirm that the component library is shared and must remain backward-compatible.

2. Design Component API and Data Model

Define props for the notification component (e.g., type, message, duration, onDismiss) and the notification data model (id, type, message, timestamp, read status). Consider how to integrate with the shared library.

3. Plan State Management and Real-Time Updates

Choose a state management approach (e.g., Context + useReducer, Redux, Zustand) and describe how real-time updates (WebSocket, SSE, polling) will update the store. Discuss optimistic updates and error handling.

4. Implement Debouncing and Cross-Tab Sync

Explain debouncing strategies for frequent updates (e.g., batching notifications) and cross-tab synchronization using BroadcastChannel, localStorage events, or a service worker.

5. Summarize Trade-offs and Edge Cases

Highlight key decisions, trade-offs (e.g., performance vs. real-time, complexity of cross-tab sync), and edge cases like offline support, notification overflow, and accessibility.

Key Points to Mention

Component API design: props for customization, controlled vs. uncontrolled, and integration with shared library
Data model: notification schema, normalization, and storage (in-memory vs. persisted)
State management: centralized store, actions/reducers, and selectors for performance
Real-time updates: WebSocket/SSE integration, reconnection logic, and fallback to polling
Debouncing: batching rapid updates, throttling UI updates, and avoiding notification spam
Cross-tab sync: BroadcastChannel API, localStorage events, and conflict resolution

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.