## Introduction
Scaling React applications to enterprise level presents unique challenges. At Walmart, our Business Unit Accounting system serves over 5000 stores, processing millions of transactions daily. This post shares the architectural decisions, performance optimizations, and lessons learned from building and scaling this critical system.
## The Challenge
When I joined the Business Unit Accounting team in 2020, we faced several challenges:
- **Scale**: 5000+ stores across multiple countries
- **Performance**: Sub-second response times required
- **Reliability**: 99.9% uptime SLA
- **Complexity**: Complex financial calculations and real-time data sync
- **Team Growth**: Scaling from a small team to multiple squads
## Architecture Overview
### Frontend Architecture
We built the system using modern React patterns:
```javascript
// Example: Optimized data fetching with React Query
import { useQuery } from 'react-query'
function StoreTransactions({ storeId }) {
const { data, isLoading } = useQuery(
['transactions', storeId],
() => fetchTransactions(storeId),
{
staleTime: 5000,
cacheTime: 300000,
}
)
return
}
```
### State Management
We used Redux with Redux Saga for complex async flows:
- **Redux** for predictable state management
- **Redux Saga** for side effects and API orchestration
- **Reselect** for memoized selectors
- **Immer** for immutable updates
### Backend Integration
Our Scala backend provided:
- RESTful APIs with sub-100ms response times
- GraphQL for complex queries
- WebSocket connections for real-time updates
- Event-driven architecture with Kafka
## Performance Optimizations
### 1. Code Splitting
We implemented route-based code splitting:
```javascript
const Reports = lazy(() => import('./Reports'))
const Analytics = lazy(() => import('./Analytics'))
```
**Results:**
- Initial bundle size reduced by 60%
- Time to Interactive improved from 4.2s to 1.8s
### 2. Virtualization
For large data tables:
```javascript
import { FixedSizeList } from 'react-window'
function TransactionList({ transactions }) {
return (
{({ index, style }) => (
)}
)
}
```
### 3. Memoization
Using React.memo and useMemo strategically:
```javascript
const ExpensiveComponent = React.memo(({ data }) => {
const processedData = useMemo(
() => complexCalculation(data),
[data]
)
return
})
```
## Key Learnings
### 1. Start with Performance in Mind
- Set up performance budgets early
- Monitor bundle sizes in CI/CD
- Use Lighthouse CI for automated testing
### 2. Embrace TypeScript
TypeScript caught countless bugs before production:
```typescript
interface Transaction {
id: string
amount: number
storeId: string
timestamp: Date
}
function processTransaction(tx: Transaction): Result {
// Type-safe processing
}
```
### 3. Test Coverage Matters
We maintained 85%+ test coverage:
- Unit tests with Jest
- Integration tests with React Testing Library
- E2E tests with TestCafe
### 4. Documentation is Code
We treated documentation as first-class:
- Storybook for component library
- Auto-generated API docs
- Architecture decision records (ADRs)
## Monitoring & Observability
We implemented comprehensive monitoring:
- **Performance**: Real User Monitoring (RUM)
- **Errors**: Sentry for error tracking
- **Metrics**: Custom dashboards in Grafana
- **Logs**: Centralized logging with ELK stack
## Results
After 4 years of development and optimization:
- **99.9% uptime** achieved
- **5000+ stores** using the system
- **60% reduction** in financial reconciliation time
- **$10B+ transactions** processed annually
- **Sub-2s load times** across all modules
## Conclusion
Scaling React applications to enterprise level requires:
1. **Strong architecture** foundation
2. **Performance optimization** from day one
3. **Comprehensive testing** strategy
4. **Monitoring and observability**
5. **Team collaboration** and knowledge sharing
The journey taught me that scaling isn't just about technology—it's about people, processes, and continuous improvement.
## Resources
- [React Performance Optimization](https://react.dev/learn/render-and-commit)
- [Redux Best Practices](https://redux.js.org/style-guide/)
- [Walmart Tech Blog](https://medium.com/walmartglobaltech)
---
**Want to discuss React architecture or scaling challenges?** Feel free to [reach out](/contact) or connect with me on [LinkedIn](https://linkedin.com/in/vinayrajput).
