johnnystefan/pattern-proxy

Skill: Implement Proxy Pattern

Purpose

Provides a substitute or placeholder for another object to control access to it (e.g., lazy loading, logging, access control).

Procedural Instructions

1. Define Service Interface: Create an interface that both the real service and the proxy will follow.
2. Create Real Service: The class that performs the actual business logic.
3. Create Proxy: Implements the same interface, maintains a reference to the service, and controls access/execution.

TypeScript Example

interface Subject {
  request(): void;
}

class RealSubject implements Subject {
  request() {
    console.log('RealSubject handling request');
  }
}

class ProxySubject implements Subject {
  private realSubject: RealSubject | null = null;

  request() {
    if (this.checkAccess()) {
      if (!this.realSubject) this.realSubject = new RealSubject(); // Lazy Init
      this.realSubject.request();
      this.logAccess();
    }
  }

  private checkAccess(): boolean {
    return true;
  }
  private logAccess() {
    console.log('Proxy: Logging request');
  }
}

Payoff

• Control: Manage service lifecycle and access without modifying the service class.
• Robustness: The proxy works even if the service isn't ready or available.