Codexpal - Learn Programming Interactively

Lesson Content

Introduction to Design Patterns

Design patterns are reusable solutions to common problems in software design. They provide templates for solving recurring design challenges.

Types of Design Patterns

Creational - Object creation patterns (Singleton, Factory, Builder)
Structural - Object composition patterns (Adapter, Decorator, Facade)
Behavioral - Communication patterns (Observer, Strategy, Command)

Why Use Design Patterns?

✅ Proven solutions to common problems
✅ Improve code reusability
✅ Make code more maintainable
✅ Enhance communication between developers
✅ Follow best practices

Pattern Structure

Most patterns have:

Problem - What problem does it solve?
Solution - How does it solve it?
Consequences - Trade-offs and benefits

Example Code

Compare code with and without patterns

// Without pattern - tightly coupled
class User {
  constructor(name) {
    this.name = name;
    this.emailService = new EmailService(); // Tight coupling
  }
  
  sendEmail(message) {
    this.emailService.send(this.name, message);
  }
}

// With pattern - loosely coupled (Dependency Injection)
class UserWithPattern {
  constructor(name, emailService) {
    this.name = name;
    this.emailService = emailService; // Loose coupling
  }
  
  sendEmail(message) {
    this.emailService.send(this.name, message);
  }
}

console.log('Pattern helps with:', 'Loose coupling, Testability, Flexibility');

Expected Output:

Pattern helps with: Loose coupling, Testability, Flexibility

Study Tips

•Read the theory content thoroughly before practicing
•Review the example code to understand key concepts
•Proceed to the Practice tab when you're ready to code