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Part 190 of 354

📘 Express.js with TypeScript: Web Framework

Master express.js with typescript: web framework in TypeScript with practical examples, best practices, and real-world applications 🚀

🚀Intermediate
25 min read

Prerequisites

  • Basic understanding of JavaScript 📝
  • TypeScript installation ⚡
  • VS Code or preferred IDE 💻

What you'll learn

  • Understand the concept fundamentals 🎯
  • Apply the concept in real projects 🏗️
  • Debug common issues 🐛
  • Write type-safe code ✨

🎯 Introduction

Welcome to this exciting tutorial on Express.js with TypeScript! 🎉 In this guide, we’ll explore how to build powerful web applications using Express.js and TypeScript together.

You’ll discover how Express.js can transform your TypeScript development experience when building APIs 🌐, web servers 🖥️, or backend services 📚. Whether you’re creating REST APIs, handling middleware, or managing routes, understanding Express.js with TypeScript is essential for writing robust, maintainable server-side code.

By the end of this tutorial, you’ll feel confident building production-ready web applications with Express.js and TypeScript! Let’s dive in! 🏊‍♂️

📚 Understanding Express.js with TypeScript

🤔 What is Express.js?

Express.js is like the Swiss Army knife of web development 🔧. Think of it as a friendly waiter in a restaurant who takes orders (HTTP requests), communicates with the kitchen (your application logic), and serves the food (HTTP responses).

In TypeScript terms, Express.js provides a minimal and flexible Node.js web application framework 🚀. This means you can:

  • ✨ Create RESTful APIs with ease
  • 🚀 Handle HTTP requests and responses
  • 🛡️ Implement middleware for cross-cutting concerns
  • 📊 Manage routing and URL patterns

💡 Why Use Express.js with TypeScript?

Here’s why developers love Express.js with TypeScript:

  1. Type Safety 🔒: Catch errors at compile-time for requests and responses
  2. Better IDE Support 💻: Autocomplete for Express methods and middleware
  3. Code Documentation 📖: Types serve as inline docs for your API
  4. Refactoring Confidence 🔧: Change code without fear of breaking things

Real-world example: Imagine building an e-commerce API 🛒. With Express.js and TypeScript, you can define typed routes for products, orders, and users, ensuring your API is both fast and safe.

🔧 Basic Syntax and Usage

📝 Simple Example

Let’s start with a friendly example:

// 👋 Hello, Express with TypeScript!
import express, { Application, Request, Response } from 'express';

// 🎨 Create our Express app
const app: Application = express();
const port: number = 3000;

// 🔧 Middleware for parsing JSON
app.use(express.json());

// 🎯 Simple route
app.get('/', (req: Request, res: Response) => {
  res.json({ message: 'Welcome to Express with TypeScript! 🚀' });
});

// 🚀 Start the server
app.listen(port, () => {
  console.log(`🌟 Server running at http://localhost:${port}`);
});

💡 Explanation: Notice how we import specific types from Express! The Application, Request, and Response types help us write type-safe server code.

🎯 Common Patterns

Here are patterns you’ll use daily:

// 🏗️ Pattern 1: Typed route parameters
interface UserParams {
  id: string;
}

app.get('/users/:id', (req: Request<UserParams>, res: Response) => {
  const userId = req.params.id; // 🎯 TypeScript knows this is a string!
  res.json({ userId, message: `Hello user ${userId}! 👋` });
});

// 🎨 Pattern 2: Request body typing
interface CreateUserBody {
  name: string;
  email: string;
  age: number;
}

app.post('/users', (req: Request<{}, {}, CreateUserBody>, res: Response) => {
  const { name, email, age } = req.body; // 🛡️ All typed!
  res.json({ message: `Created user ${name}! ✨` });
});

// 🔄 Pattern 3: Custom middleware
const loggerMiddleware = (req: Request, res: Response, next: express.NextFunction) => {
  console.log(`📝 ${req.method} ${req.path} at ${new Date().toISOString()}`);
  next(); // 🚀 Continue to next middleware
};

app.use(loggerMiddleware);

💡 Practical Examples

🛒 Example 1: E-commerce API

Let’s build something real:

// 🛍️ Define our product types
interface Product {
  id: string;
  name: string;
  price: number;
  category: string;
  emoji: string;
  inStock: boolean;
}

interface CreateProductBody {
  name: string;
  price: number;
  category: string;
  emoji: string;
}

// 📦 Mock database
const products: Product[] = [
  { id: '1', name: 'TypeScript Book', price: 29.99, category: 'books', emoji: '📘', inStock: true },
  { id: '2', name: 'Coffee Mug', price: 12.99, category: 'accessories', emoji: '☕', inStock: true }
];

// 🎯 Product routes
class ProductController {
  // 📋 Get all products
  static getProducts = (req: Request, res: Response) => {
    console.log('🛒 Fetching all products');
    res.json({
      success: true,
      data: products,
      count: products.length
    });
  };

  // 🔍 Get product by ID
  static getProductById = (req: Request<{ id: string }>, res: Response) => {
    const { id } = req.params;
    const product = products.find(p => p.id === id);
    
    if (!product) {
      return res.status(404).json({
        success: false,
        message: `Product with ID ${id} not found 😔`
      });
    }
    
    console.log(`📦 Found product: ${product.emoji} ${product.name}`);
    res.json({
      success: true,
      data: product
    });
  };

  // ➕ Create new product
  static createProduct = (req: Request<{}, {}, CreateProductBody>, res: Response) => {
    const { name, price, category, emoji } = req.body;
    
    const newProduct: Product = {
      id: (products.length + 1).toString(),
      name,
      price,
      category,
      emoji,
      inStock: true
    };
    
    products.push(newProduct);
    console.log(`✨ Created product: ${emoji} ${name}`);
    
    res.status(201).json({
      success: true,
      data: newProduct,
      message: 'Product created successfully! 🎉'
    });
  };
}

// 🚀 Set up routes
app.get('/api/products', ProductController.getProducts);
app.get('/api/products/:id', ProductController.getProductById);
app.post('/api/products', ProductController.createProduct);

🎯 Try it yourself: Add a updateProduct method and a deleteProduct method!

🎮 Example 2: Gaming Leaderboard API

Let’s make it fun:

// 🏆 Game score types
interface GameScore {
  playerId: string;
  playerName: string;
  score: number;
  level: number;
  achievements: string[];
  timestamp: Date;
}

interface SubmitScoreBody {
  playerId: string;
  playerName: string;
  score: number;
  level: number;
}

// 🎮 Mock leaderboard data
const leaderboard: GameScore[] = [
  {
    playerId: '1',
    playerName: 'TypeScript Master',
    score: 9999,
    level: 50,
    achievements: ['🌟 First Steps', '🏆 High Scorer', '🚀 Speed Demon'],
    timestamp: new Date()
  }
];

class GameController {
  // 📊 Get leaderboard
  static getLeaderboard = (req: Request, res: Response) => {
    const sortedScores = leaderboard
      .sort((a, b) => b.score - a.score)
      .slice(0, 10); // 🎯 Top 10 players
    
    console.log('🏆 Fetching leaderboard');
    res.json({
      success: true,
      data: sortedScores,
      message: 'Top players retrieved! 🌟'
    });
  };

  // 🎮 Submit new score
  static submitScore = (req: Request<{}, {}, SubmitScoreBody>, res: Response) => {
    const { playerId, playerName, score, level } = req.body;
    
    // 🔍 Check if player exists
    const existingPlayerIndex = leaderboard.findIndex(p => p.playerId === playerId);
    
    if (existingPlayerIndex !== -1) {
      // 📈 Update existing player
      const existingPlayer = leaderboard[existingPlayerIndex];
      if (score > existingPlayer.score) {
        existingPlayer.score = score;
        existingPlayer.level = level;
        existingPlayer.timestamp = new Date();
        existingPlayer.achievements.push('🎊 New High Score');
        
        console.log(`🎉 ${playerName} set a new high score: ${score}!`);
        res.json({
          success: true,
          data: existingPlayer,
          message: 'New high score! 🏆'
        });
      } else {
        res.json({
          success: true,
          message: 'Score submitted but not a new high score 😅'
        });
      }
    } else {
      // ➕ Add new player
      const newScore: GameScore = {
        playerId,
        playerName,
        score,
        level,
        achievements: ['🌟 First Game'],
        timestamp: new Date()
      };
      
      leaderboard.push(newScore);
      console.log(`✨ Welcome new player: ${playerName}!`);
      
      res.status(201).json({
        success: true,
        data: newScore,
        message: 'Welcome to the leaderboard! 🎮'
      });
    }
  };
}

// 🚀 Game routes
app.get('/api/leaderboard', GameController.getLeaderboard);
app.post('/api/scores', GameController.submitScore);

🚀 Advanced Concepts

🧙‍♂️ Advanced Topic 1: Custom Middleware

When you’re ready to level up, try this advanced pattern:

// 🎯 Authentication middleware
interface AuthenticatedRequest extends Request {
  user?: {
    id: string;
    name: string;
    role: 'admin' | 'user';
  };
}

const authenticateToken = (req: AuthenticatedRequest, res: Response, next: express.NextFunction) => {
  const authHeader = req.headers.authorization;
  const token = authHeader && authHeader.split(' ')[1];
  
  if (!token) {
    return res.status(401).json({
      success: false,
      message: 'Access token required 🔐'
    });
  }
  
  // 🔍 Mock token verification
  if (token === 'valid-token') {
    req.user = {
      id: '1',
      name: 'John Doe',
      role: 'user'
    };
    next();
  } else {
    res.status(403).json({
      success: false,
      message: 'Invalid token 🚫'
    });
  }
};

// 🛡️ Protected route
app.get('/api/protected', authenticateToken, (req: AuthenticatedRequest, res: Response) => {
  res.json({
    success: true,
    message: `Welcome ${req.user?.name}! 🎉`,
    data: { userId: req.user?.id }
  });
});

🏗️ Advanced Topic 2: Error Handling

For the brave developers:

// 🚀 Custom error class
class AppError extends Error {
  statusCode: number;
  isOperational: boolean;

  constructor(message: string, statusCode: number) {
    super(message);
    this.statusCode = statusCode;
    this.isOperational = true;
    
    Error.captureStackTrace(this, this.constructor);
  }
}

// 🎯 Global error handler
const globalErrorHandler = (
  error: AppError,
  req: Request,
  res: Response,
  next: express.NextFunction
) => {
  const { statusCode = 500, message } = error;
  
  console.error(`💥 Error occurred: ${message}`);
  
  res.status(statusCode).json({
    success: false,
    message: message || 'Something went wrong! 😰',
    ...(process.env.NODE_ENV === 'development' && { stack: error.stack })
  });
};

// 🛡️ Use error handler
app.use(globalErrorHandler);

// 🎯 Async error wrapper
const asyncHandler = (fn: Function) => {
  return (req: Request, res: Response, next: express.NextFunction) => {
    Promise.resolve(fn(req, res, next)).catch(next);
  };
};

⚠️ Common Pitfalls and Solutions

😱 Pitfall 1: Not Typing Request Bodies

// ❌ Wrong way - losing all type safety!
app.post('/users', (req: Request, res: Response) => {
  const userData = req.body; // 💥 Could be anything!
  const name = userData.name; // 😰 Might not exist!
});

// ✅ Correct way - embrace the types!
interface CreateUserBody {
  name: string;
  email: string;
}

app.post('/users', (req: Request<{}, {}, CreateUserBody>, res: Response) => {
  const { name, email } = req.body; // 🛡️ TypeScript knows the structure!
  console.log(`Creating user: ${name} (${email})`);
});

🤯 Pitfall 2: Forgetting Error Handling

// ❌ Dangerous - unhandled promise rejection!
app.get('/users/:id', async (req: Request, res: Response) => {
  const user = await getUserFromDatabase(req.params.id); // 💥 Might throw!
  res.json(user);
});

// ✅ Safe - proper error handling!
app.get('/users/:id', async (req: Request, res: Response) => {
  try {
    const user = await getUserFromDatabase(req.params.id);
    res.json({ success: true, data: user });
  } catch (error) {
    console.error('⚠️ Error fetching user:', error);
    res.status(500).json({
      success: false,
      message: 'Failed to fetch user 😔'
    });
  }
});

🛠️ Best Practices

  1. 🎯 Type Everything: Request bodies, params, responses - type them all!
  2. 📝 Use Interfaces: Define clear contracts for your API
  3. 🛡️ Handle Errors: Always have proper error handling
  4. 🎨 Organize Routes: Use controllers and routers for better structure
  5. ✨ Validate Input: Always validate and sanitize user input

🧪 Hands-On Exercise

🎯 Challenge: Build a Library Management API

Create a type-safe library management system:

📋 Requirements:

  • ✅ Books with title, author, ISBN, and availability
  • 🏷️ Categories for books (fiction, non-fiction, technical)
  • 👤 User borrowing and returning books
  • 📅 Due dates and overdue notifications
  • 🎨 Each book needs an emoji category icon!

🚀 Bonus Points:

  • Add book search functionality
  • Implement borrowing limits per user
  • Create overdue fine calculations

💡 Solution

🔍 Click to see solution
// 🎯 Our type-safe library system!
interface Book {
  id: string;
  title: string;
  author: string;
  isbn: string;
  category: 'fiction' | 'non-fiction' | 'technical';
  emoji: string;
  available: boolean;
  borrowedBy?: string;
  dueDate?: Date;
}

interface BorrowBookBody {
  userId: string;
  bookId: string;
}

interface User {
  id: string;
  name: string;
  borrowedBooks: string[];
  maxBooks: number;
}

class LibraryController {
  private static books: Book[] = [
    {
      id: '1',
      title: 'TypeScript Handbook',
      author: 'Microsoft',
      isbn: '978-1234567890',
      category: 'technical',
      emoji: '📘',
      available: true
    },
    {
      id: '2',
      title: 'The Great Gatsby',
      author: 'F. Scott Fitzgerald',
      isbn: '978-0743273565',
      category: 'fiction',
      emoji: '📚',
      available: true
    }
  ];

  private static users: User[] = [
    { id: '1', name: 'Alice', borrowedBooks: [], maxBooks: 3 }
  ];

  // 📚 Get all books
  static getBooks = (req: Request, res: Response) => {
    const { category, available } = req.query;
    let filteredBooks = LibraryController.books;

    if (category) {
      filteredBooks = filteredBooks.filter(book => book.category === category);
    }

    if (available !== undefined) {
      const isAvailable = available === 'true';
      filteredBooks = filteredBooks.filter(book => book.available === isAvailable);
    }

    res.json({
      success: true,
      data: filteredBooks,
      count: filteredBooks.length
    });
  };

  // 📖 Borrow a book
  static borrowBook = (req: Request<{}, {}, BorrowBookBody>, res: Response) => {
    const { userId, bookId } = req.body;
    
    const user = LibraryController.users.find(u => u.id === userId);
    const book = LibraryController.books.find(b => b.id === bookId);
    
    if (!user) {
      return res.status(404).json({
        success: false,
        message: 'User not found 😔'
      });
    }
    
    if (!book) {
      return res.status(404).json({
        success: false,
        message: 'Book not found 😔'
      });
    }
    
    if (!book.available) {
      return res.status(400).json({
        success: false,
        message: 'Book is not available 📵'
      });
    }
    
    if (user.borrowedBooks.length >= user.maxBooks) {
      return res.status(400).json({
        success: false,
        message: 'Maximum book limit reached 📚'
      });
    }
    
    // 🎉 Borrow the book
    book.available = false;
    book.borrowedBy = userId;
    book.dueDate = new Date(Date.now() + 14 * 24 * 60 * 60 * 1000); // 14 days
    user.borrowedBooks.push(bookId);
    
    res.json({
      success: true,
      message: `Successfully borrowed ${book.emoji} ${book.title}! 🎉`,
      data: {
        book,
        dueDate: book.dueDate
      }
    });
  };

  // 📤 Return a book
  static returnBook = (req: Request<{ bookId: string }>, res: Response) => {
    const { bookId } = req.params;
    const book = LibraryController.books.find(b => b.id === bookId);
    
    if (!book || book.available) {
      return res.status(400).json({
        success: false,
        message: 'Book is not currently borrowed 🤔'
      });
    }
    
    const user = LibraryController.users.find(u => u.id === book.borrowedBy);
    if (user) {
      user.borrowedBooks = user.borrowedBooks.filter(id => id !== bookId);
    }
    
    book.available = true;
    book.borrowedBy = undefined;
    book.dueDate = undefined;
    
    res.json({
      success: true,
      message: `Successfully returned ${book.emoji} ${book.title}! ✨`,
      data: book
    });
  };
}

// 🚀 Library routes
app.get('/api/books', LibraryController.getBooks);
app.post('/api/books/borrow', LibraryController.borrowBook);
app.post('/api/books/:bookId/return', LibraryController.returnBook);

🎓 Key Takeaways

You’ve learned so much! Here’s what you can now do:

  • Create Express.js APIs with TypeScript confidence 💪
  • Avoid common mistakes that trip up beginners 🛡️
  • Apply best practices in real projects 🎯
  • Debug issues like a pro 🐛
  • Build awesome web applications with Express.js and TypeScript! 🚀

Remember: Express.js with TypeScript is your powerful duo for building robust web applications! It’s here to help you create amazing APIs and web services. 🤝

🤝 Next Steps

Congratulations! 🎉 You’ve mastered Express.js with TypeScript!

Here’s what to do next:

  1. 💻 Practice with the exercises above
  2. 🏗️ Build a small API project using Express.js and TypeScript
  3. 📚 Move on to our next tutorial: Database Integration with TypeScript
  4. 🌟 Share your learning journey with others!

Remember: Every Express.js expert was once a beginner. Keep coding, keep learning, and most importantly, have fun building amazing web applications! 🚀


Happy coding! 🎉🚀✨