express

Express.js Framework Patterns

Purpose

Essential Express.js patterns for building scalable backend APIs, emphasizing clean routing, middleware composition, and proper request/response handling.

When to Use This Skill

• Creating or modifying Express routes
• Building middleware (auth, validation, error handling)
• Working with Express Request/Response objects
• Implementing BaseController pattern
• Error handling in Express

---

Clean Route Pattern

Routes Only Route

Routes should ONLY:

• ✅ Define route paths
• ✅ Register middleware
• ✅ Delegate to controllers

Routes should NEVER:

• ❌ Contain business logic
• ❌ Access database directly
• ❌ Implement validation logic
• ❌ Format complex responses

import { Router } from 'express';
import { UserController } from '../controllers/UserController';
import { SSOMiddlewareClient } from '../middleware/SSOMiddleware';

const router = Router();
const controller = new UserController();

// Clean delegation - no business logic
router.get('/:id',
    SSOMiddlewareClient.verifyLoginStatus,
    async (req, res) => controller.getUser(req, res)
);

router.post('/',
    SSOMiddlewareClient.verifyLoginStatus,
    async (req, res) => controller.createUser(req, res)
);

export default router;

---

BaseController Pattern

Implementation

import * as Sentry from '@sentry/node';
import { Response } from 'express';

export abstract class BaseController {
    protected handleError(
        error: unknown,
        res: Response,
        context: string,
        statusCode = 500
    ): void {
        Sentry.withScope((scope) => {
            scope.setTag('controller', this.constructor.name);
            scope.setTag('operation', context);
            Sentry.captureException(error);
        });

        res.status(statusCode).json({
            success: false,
            error: {
                message: error instanceof Error ? error.message : 'An error occurred',
                code: statusCode,
            },
        });
    }

    protected handleSuccess<T>(
        res: Response,
        data: T,
        message?: string,
        statusCode = 200
    ): void {
        res.status(statusCode).json({
            success: true,
            message,
            data,
        });
    }

    protected async withTransaction<T>(
        name: string,
        operation: string,
        callback: () => Promise<T>
    ): Promise<T> {
        return await Sentry.startSpan({ name, op: operation }, callback);
    }

    protected addBreadcrumb(
        message: string,
        category: string,
        data?: Record<string, any>
    ): void {
        Sentry.addBreadcrumb({ message, category, level: 'info', data });
    }
}