README.md

Proxy Pattern

The Proxy pattern puts a stand-in in front of the real object. The caller interacts with the proxy, which can add access control, logging, caching, or lazy loading before (and after) delegating to the actual implementation.

Example

class RealSubject {
  request() {
    console.log("RealSubject: Handling request.");
  }
}

class Proxy {
  constructor(realSubject) {
    this.realSubject = realSubject;
  }

  request() {
    if (this.checkAccess()) {
      this.realSubject.request();
      this.logAccess();
    }
  }

  checkAccess() {
    console.log("Proxy: Checking access prior to firing a real request.");
    // Simulate access check
    return true;
  }

  logAccess() {
    console.log("Proxy: Logging the time of request.");
  }
}

Explaining the code

1. RealSubject Class:

   • This class represents the real object that performs the actual work. It has a request method that logs a message indicating it is handling the request.

2. Proxy Class:

   • This class acts as a proxy to the RealSubject. It holds a reference to an instance of RealSubject and controls access to it.
   • The request method in the Proxy class first checks access by calling checkAccess. If access is granted, it forwards the request to the RealSubject and then logs the access by calling logAccess.

Usage

const realSubject = new RealSubject();
const proxy = new Proxy(realSubject);

proxy.request();

• An instance of RealSubject is created.
• An instance of Proxy is created, with the RealSubject instance passed to its constructor.
• The request method is called on the Proxy instance. This triggers the access check, forwards the request to the RealSubject if access is granted, and logs the access.

Summary

RealSubject doesn't know it's being proxied; it just handles requests. All the cross-cutting concerns (access checks, logging) live in the proxy. This keeps each class focused on one job, and you can add or change proxy behavior without ever touching the underlying implementation.