---

name: pitfalls-express-api description: "Express API conventions and storage patterns. Use when building REST APIs, defining routes, or implementing storage interfaces. Triggers on: Express, router, API route, status code, storage interface."

Express API Pitfalls

Common pitfalls and correct patterns for Express APIs.

When to Use

• Building REST API routes
• Implementing storage interfaces
• Setting HTTP status codes
• Validating request bodies
• Reviewing Express API code

Workflow

Step 1: Verify Route Structure

Check that routes follow REST conventions.

Step 2: Check Status Codes

Ensure correct status codes for each operation.

Step 3: Verify Validation

Confirm input validation middleware is in place.

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Route Structure

Copy// Public routes
GET  /api/resource          // List
GET  /api/resource/:id      // Get one

// Admin routes (with auth middleware)
POST   /api/admin/resource      // Create (201)
PATCH  /api/admin/resource/:id  // Update (200)
DELETE /api/admin/resource/:id  // Delete (204)

// ✅ Always validate before storage
router.post('/', validateBody(schema), async (req, res) => {
  const validated = req.body; // Already validated by middleware
});

Status Codes

Storage Interface Pattern

Copy// ✅ Define interface for all storage operations
interface IStorage {
  // Strategies
  getStrategies(): Promise<Strategy[]>;
  getStrategy(id: string): Promise<Strategy | undefined>;
  createStrategy(data: NewStrategy): Promise<Strategy>;
  updateStrategy(id: string, data: Partial<Strategy>): Promise<Strategy | undefined>;
  deleteStrategy(id: string): Promise<boolean>;
}

// ✅ Implement for different backends
class DbStorage implements IStorage { ... }  // PostgreSQL
class MemStorage implements IStorage { ... } // Testing

Background Job Patterns

Copy// ✅ Cleanup on process exit
const intervals: NodeJS.Timeout[] = [];

function startJob(fn: () => void, ms: number) {
  const id = setInterval(fn, ms);
  intervals.push(id);
  return id;
}

process.on('SIGTERM', () => {
  intervals.forEach(clearInterval);
  process.exit(0);
});

// ✅ Handle overlapping executions
let isRunning = false;
async function scanForOpportunities() {
  if (isRunning) return;
  isRunning = true;
  try {
    await scan();
  } finally {
    isRunning = false;
  }
}

Quick Checklist

• Routes follow REST conventions
• Correct status codes returned
• Input validation on all endpoints
• Storage interface abstraction used
• Background jobs handle cleanup