●React + Fintech

React dominates fintech frontend development for one simple reason: the ecosystem has solved the hard problems. Real-time data synchronization, complex form validation, accessible data tables, and secure payment flows all have battle-tested React implementations. You're not building infrastructure—you're composing proven solutions. The component model maps naturally to financial UI patterns. A stock ticker, an order book, a portfolio chart—these are discrete units with clear data dependencies and render boundaries. React's reconciliation algorithm ensures efficient updates when prices change 10 times per second. Suspense boundaries let you prioritize what renders first: show the account balance immediately, stream in the transaction history, load charts last. For fintech specifically, React's controlled component pattern is essential for PCI compliance. You maintain precise control over when and how sensitive data flows through the application. Combined with TypeScript, you get compile-time guarantees that card numbers can't accidentally leak into logging or analytics. The testing story seals the deal: React Testing Library encourages tests that verify user behavior, not implementation details. When regulators ask 'how do you ensure transfers go to the right account,' you can point to tests that actually fill forms and click buttons—not mocked unit tests that might drift from reality.

Fintech projects demand a security-first architecture, and I design the React application structure around that constraint from day one. Sensitive components (payment forms, account details) are isolated into modules with strict data flow rules. No card number ever touches Redux or any global state. TypeScript's type system enforces these boundaries at compile time—it's not just documentation, it's automated policy enforcement. Every fintech project starts with threat modeling: where does sensitive data enter the app, where does it exit, what happens if any component in between is compromised? This informs the component hierarchy, the state management strategy, and the testing approach. I implement Content Security Policy headers that whitelist only necessary scripts, and Subresource Integrity hashes for all third-party code—requirements for PCI-DSS 4.0 that most developers overlook. For real-time features, I architect WebSocket connections as a separate concern from React components. A subscription service manages connections, heartbeats, and reconnection. React Query subscribes to updates from this service, ensuring components don't care whether data came from REST or WebSocket—they just render the latest state. This separation makes the system testable: you can mock the subscription service without touching network code. My testing strategy for fintech emphasizes integration tests that verify complete user flows. A unit test proving a transfer form validates correctly is worthless if the submit handler has a bug. I test the entire journey: enter amount, confirm, see success, verify balance updated. These tests run against a realistic backend (not mocks) because financial logic bugs are too expensive to catch in production.