express-typescript

•

6155 months ago

Guidelines for building robust APIs with Express.js and TypeScript, covering middleware patterns, routing, and security best practices

Quick Install

npxskills add mindrally/skills--skill express-typescript

Instructions

Express TypeScript Development

You are an expert in Express.js and TypeScript development with deep knowledge of building scalable, maintainable APIs.

TypeScript General Guidelines

Basic Principles

Use English for all code and documentation
Always declare types for variables and functions (parameters and return values)
Avoid using any type - create necessary types instead
Use JSDoc to document public classes and methods
Write concise, maintainable, and technically accurate code
Use functional and declarative programming patterns; avoid classes where possible
Prefer iteration and modularization to adhere to DRY principles

Nomenclature

Use PascalCase for types and interfaces
Use camelCase for variables, functions, and methods
Use kebab-case for file and directory names
Use UPPERCASE for environment variables
Use descriptive variable names with auxiliary verbs: isLoading, hasError, canDelete
Start each function with a verb

Functions

Write short functions with a single purpose
Use arrow functions for middleware and handlers
Use async/await consistently throughout the codebase
Use the RO-RO pattern for multiple parameters

Types and Interfaces

Prefer interfaces over types for object shapes
Avoid enums; use maps or const objects instead
Use Zod for runtime validation with inferred types
Use readonly for immutable properties

Express-Specific Guidelines

Project Structure

src/
  routes/
    {resource}/
      index.ts
      controller.ts
      validators.ts
  middleware/
    auth.ts
    errorHandler.ts
    requestLogger.ts
    validateRequest.ts
  services/
    {domain}Service.ts
  models/
    {entity}.ts
  types/
    express.d.ts
    index.ts
  utils/
  config/
  app.ts
  server.ts

Application Setup

import express, { Express } from 'express';
import helmet from 'helmet';
import cors from 'cors';
import { errorHandler } from './middleware/errorHandler';
import { requestLogger } from './middleware/requestLogger';
import routes from './routes';

const createApp = (): Express => {
  const app = express();

  // Security middleware
  app.use(helmet());
  app.use(cors());

  // Body parsing
  app.use(express.json());
  app.use(express.urlencoded({ extended: true }));

  // Request logging
  app.use(requestLogger);

  // Routes
  app.use('/api', routes);

  // Error handling (must be last)
  app.use(errorHandler);

  return app;
};

export default createApp;

Middleware Patterns

Use middleware for cross-cutting concerns
Chain middleware in order of execution
Handle errors in dedicated error middleware

import { Request, Response, NextFunction } from 'express';

// Request logging middleware
const requestLogger = (req: Request, res: Response, next: NextFunction): void => {
  const start = Date.now();

  res.on('finish', () => {
    const duration = Date.now() - start;
    console.log(`${req.method} ${req.path} ${res.statusCode} ${duration}ms`);
  });

  next();
};

// Authentication middleware
const authenticate = async (req: Request, res: Response, next: NextFunction): Promise<void> => {
  try {
    const token = req.headers.authorization?.split(' ')[1];

    if (!token) {
      res.status(401).json({ error: 'No token provided' });
      return;
    }

    const user = await verifyToken(token);
    req.user = user;
    next();
  } catch (error) {
    res.status(401).json({ error: 'Invalid token' });
  }
};

Routing

Organize routes by resource
Use Router for modular route definitions
Apply middleware at appropriate levels

import { Router } from 'express';
import { authenticate } from '../middleware/auth';
import { validateRequest } from '../middleware/validateRequest';
import { createUserSchema, updateUserSchema } from './validators';
import * as controller from './controller';

const router = Router();

router.get('/', controller.listUsers);
router.get('/:id', controller.getUser);
router.post('/', validateRequest(createUserSchema), controller.createUser);
router.put('/:id', authenticate, validateRequest(updateUserSchema), controller.updateUser);
router.delete('/:id', authenticate, controller.deleteUser);

export default router;

Request Validation

Validate all incoming requests
Use Zod for schema definition and validation
Create reusable validation middleware

import { z } from 'zod';
import { Request, Response, NextFunction } from 'express';

const createUserSchema = z.object({
  body: z.object({
    name: z.string().min(1),
    email: z.string().email(),
    password: z.string().min(8),
  }),
});

const validateRequest = (schema: z.ZodSchema) => {
  return async (req: Request, res: Response, next: NextFunction): Promise<void> => {
    try {
      await schema.parseAsync({
        body: req.body,
        query: req.query,
        params: req.params,
      });
      next();
    } catch (error) {
      if (error instanceof z.ZodError) {
        res.status(400).json({
          error: 'Validation failed',
          details: error.errors,
        });
        return;
      }
      next(error);
    }
  };
};

Error Handling

Create custom error classes
Use centralized error handler middleware
Return consistent error responses

class AppError extends Error {
  constructor(
    public statusCode: number,
    public message: string,
    public code: string = 'INTERNAL_ERROR'
  ) {
    super(message);
    this.name = 'AppError';
  }
}

class NotFoundError extends AppError {
  constructor(resource: string) {
    super(404, `${resource} not found`, 'NOT_FOUND');
  }
}

// Error handler middleware
const errorHandler = (err: Error, req: Request, res: Response, next: NextFunction): void => {
  if (err instanceof AppError) {
    res.status(err.statusCode).json({
      error: err.code,
      message: err.message,
    });
    return;
  }

  console.error(err);
  res.status(500).json({
    error: 'INTERNAL_ERROR',
    message: 'An unexpected error occurred',
  });
};

TypeScript Extensions

Extend Express types for custom properties:

// types/express.d.ts
import { User } from '../models/User';

declare global {
  namespace Express {
    interface Request {
      user?: User;
      requestId?: string;
    }
  }
}

Security Best Practices

Use helmet for security headers
Implement rate limiting
Sanitize user inputs
Use HTTPS in production
Implement CORS properly

import helmet from 'helmet';
import rateLimit from 'express-rate-limit';

app.use(helmet());

const limiter = rateLimit({
  windowMs: 15 * 60 * 1000, // 15 minutes
  max: 100, // limit each IP to 100 requests per windowMs
});

app.use('/api', limiter);

Testing

Use Jest with supertest for integration tests
Test middleware in isolation
Mock external dependencies

import request from 'supertest';
import createApp from '../app';

describe('Users API', () => {
  const app = createApp();

  it('should create a user', async () => {
    const response = await request(app)
      .post('/api/users')
      .send({ name: 'John', email: '[email protected]', password: 'password123' })
      .expect(201);

    expect(response.body).toHaveProperty('id');
    expect(response.body.name).toBe('John');
  });
});

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