express

Development

Express.js middleware patterns, routing, error handling, security, and production best practices.

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Express Skill

Expert assistance for building Node.js APIs with Express.js.

Capabilities

Configure Express applications with middleware
Implement RESTful routing patterns
Handle errors with custom middleware
Apply security best practices
Set up validation and parsing
Configure production deployments

Usage

Invoke this skill when you need to:

Build REST APIs with Express
Implement middleware pipelines
Handle errors gracefully
Add authentication/authorization
Set up API documentation

Inputs

Parameter	Type	Required	Description
routePath	string	Yes	Route path prefix
methods	array	Yes	HTTP methods
middleware	array	No	Middleware to apply
validation	boolean	No	Add validation

Patterns

Application Setup

// src/app.ts
import express, { Express, Request, Response, NextFunction } from 'express';
import cors from 'cors';
import helmet from 'helmet';
import compression from 'compression';
import morgan from 'morgan';
import { rateLimit } from 'express-rate-limit';

import { errorHandler, notFoundHandler } from './middleware/error';
import { usersRouter } from './routes/users';
import { authRouter } from './routes/auth';

export function createApp(): Express {
  const app = express();

  // Security middleware
  app.use(helmet());
  app.use(cors({
    origin: process.env.CORS_ORIGIN || 'http://localhost:3000',
    credentials: true,
  }));

  // Rate limiting
  app.use(rateLimit({
    windowMs: 15 * 60 * 1000,
    max: 100,
    standardHeaders: true,
    legacyHeaders: false,
  }));

  // Parsing
  app.use(express.json({ limit: '10kb' }));
  app.use(express.urlencoded({ extended: true, limit: '10kb' }));

  // Compression and logging
  app.use(compression());
  app.use(morgan(process.env.NODE_ENV === 'production' ? 'combined' : 'dev'));

  // Routes
  app.use('/api/auth', authRouter);
  app.use('/api/users', usersRouter);

  // Health check
  app.get('/health', (req, res) => {
    res.json({ status: 'ok', timestamp: new Date().toISOString() });
  });

  // Error handling
  app.use(notFoundHandler);
  app.use(errorHandler);

  return app;
}

Router with Controllers

// src/routes/users.ts
import { Router } from 'express';
import { UsersController } from '../controllers/users.controller';
import { authenticate, authorize } from '../middleware/auth';
import { validate } from '../middleware/validate';
import { createUserSchema, updateUserSchema } from '../schemas/user.schema';

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

router.get('/', authenticate, controller.findAll);
router.get('/:id', authenticate, controller.findById);
router.post('/', authenticate, authorize('admin'), validate(createUserSchema), controller.create);
router.put('/:id', authenticate, validate(updateUserSchema), controller.update);
router.delete('/:id', authenticate, authorize('admin'), controller.delete);

export { router as usersRouter };

// src/controllers/users.controller.ts
import { Request, Response, NextFunction } from 'express';
import { UsersService } from '../services/users.service';

export class UsersController {
  private service = new UsersService();

  findAll = async (req: Request, res: Response, next: NextFunction) => {
    try {
      const { page = 1, limit = 10, search } = req.query;
      const users = await this.service.findAll({
        page: Number(page),
        limit: Number(limit),
        search: search as string,
      });
      res.json(users);
    } catch (error) {
      next(error);
    }
  };

  findById = async (req: Request, res: Response, next: NextFunction) => {
    try {
      const user = await this.service.findById(req.params.id);
      if (!user) {
        return res.status(404).json({ error: 'User not found' });
      }
      res.json(user);
    } catch (error) {
      next(error);
    }
  };

  create = async (req: Request, res: Response, next: NextFunction) => {
    try {
      const user = await this.service.create(req.body);
      res.status(201).json(user);
    } catch (error) {
      next(error);
    }
  };

  update = async (req: Request, res: Response, next: NextFunction) => {
    try {
      const user = await this.service.update(req.params.id, req.body);
      res.json(user);
    } catch (error) {
      next(error);
    }
  };

  delete = async (req: Request, res: Response, next: NextFunction) => {
    try {
      await this.service.delete(req.params.id);
      res.status(204).send();
    } catch (error) {
      next(error);
    }
  };
}

Middleware Patterns

// src/middleware/auth.ts
import { Request, Response, NextFunction } from 'express';
import jwt from 'jsonwebtoken';

export interface AuthRequest extends Request {
  user?: {
    id: string;
    email: string;
    role: string;
  };
}

export function authenticate(req: AuthRequest, res: Response, next: NextFunction) {
  const token = req.headers.authorization?.replace('Bearer ', '');

  if (!token) {
    return res.status(401).json({ error: 'Authentication required' });
  }

  try {
    const decoded = jwt.verify(token, process.env.JWT_SECRET!) as AuthRequest['user'];
    req.user = decoded;
    next();
  } catch {
    return res.status(401).json({ error: 'Invalid token' });
  }
}

export function authorize(...roles: string[]) {
  return (req: AuthRequest, res: Response, next: NextFunction) => {
    if (!req.user || !roles.includes(req.user.role)) {
      return res.status(403).json({ error: 'Insufficient permissions' });
    }
    next();
  };
}

// src/middleware/validate.ts
import { Request, Response, NextFunction } from 'express';
import { ZodSchema, ZodError } from 'zod';

export function validate(schema: ZodSchema) {
  return (req: Request, res: Response, next: NextFunction) => {
    try {
      schema.parse(req.body);
      next();
    } catch (error) {
      if (error instanceof ZodError) {
        return res.status(400).json({
          error: 'Validation failed',
          details: error.errors,
        });
      }
      next(error);
    }
  };
}

// src/middleware/error.ts
import { Request, Response, NextFunction } from 'express';

export class AppError extends Error {
  constructor(
    public statusCode: number,
    public message: string,
    public isOperational = true
  ) {
    super(message);
  }
}

export function notFoundHandler(req: Request, res: Response) {
  res.status(404).json({ error: 'Not found' });
}

export function errorHandler(
  err: Error,
  req: Request,
  res: Response,
  next: NextFunction
) {
  console.error(err);

  if (err instanceof AppError) {
    return res.status(err.statusCode).json({ error: err.message });
  }

  res.status(500).json({
    error: process.env.NODE_ENV === 'production'
      ? 'Internal server error'
      : err.message,
  });
}

Async Handler Wrapper

// src/utils/asyncHandler.ts
import { Request, Response, NextFunction, RequestHandler } from 'express';

type AsyncRequestHandler = (
  req: Request,
  res: Response,
  next: NextFunction
) => Promise<any>;

export function asyncHandler(fn: AsyncRequestHandler): RequestHandler {
  return (req, res, next) => {
    Promise.resolve(fn(req, res, next)).catch(next);
  };
}

// Usage
router.get('/', asyncHandler(async (req, res) => {
  const users = await usersService.findAll();
  res.json(users);
}));

Best Practices

Use middleware for cross-cutting concerns
Implement proper error handling
Validate all inputs
Apply security middleware (helmet, cors, rate limit)
Structure code with controllers and services

Target Processes

nodejs-api-development
rest-api-development
mern-stack-development
backend-architecture