Overview

The Proxy pattern places a stand-in object between the caller and the real one. The proxy implements the same interface, so callers don't notice it exists, but it can defer creation, enforce permissions, log calls, cache results, or forward the request over the network. JavaScript even ships a built-in Proxy for the same idea at the language level.

When to use it

• The real object is expensive to create and you want lazy initialization (virtual proxy).
• You need to enforce permissions or audit access before delegating (protection proxy).
• The real object lives elsewhere — another process, another service — and you want a local stand-in (remote proxy).

Example

interface Image {
  display(): void;
}

class RealImage implements Image {
  constructor(private readonly filename: string) {
    console.log(`Loading ${filename} from disk`);
  }
  display() { console.log(`Showing ${this.filename}`); }
}

class ImageProxy implements Image {
  private real?: RealImage;
  constructor(private readonly filename: string) {}

  display() {
    if (!this.real) this.real = new RealImage(this.filename);
    this.real.display();
  }
}

const image: Image = new ImageProxy("photo.png");
image.display(); // loads + shows
image.display(); // only shows