Proxy Design Pattern

Introduction

• As the name implies, the proxy pattern is a structural pattern that creates a proxy object.

• It acts as a placeholder for another object, controlling access to it.

• Usually, an object has an interface with several properties/methods that a client can access. However, an object might not be able to deal with the client's requests alone due to heavy load or constraints such as dependency on a remote source that might cause delays (e.g. network requests)

• In these situations, adding a proxy helps in dividing the load with the target object. The proxy object looks exactly like the target object. A client might not even know that they are accessing the proxy object instead of the target object.

• The proxy handles the requests from the clients and forwards them to the target object. Hence, this prevents undue pressure on the target

• The proxy can also act as a cache and store the requests. When the same request is made again, it can just return it from the cache rather than forward it to the target. This allows the target to deal with a lesser number of requests.

• The proxy pattern tries to reduce the workload on the target object. You can use it when dealing with heavy applications that perform a lot of network requests

• Since delays could occur when responding to such requests, using a proxy pattern will allow the target object to not get overburdened with requests

Use Cases

• A real-life example is HTTP requests. These are expensive operations. hence, the proxy pattern helps in reducing the number of requests forwarded to the target

Example

class GetCapital {
  getMycapital(country) {
    if (country === "Pakistan") {
      return "Islamabad";
    } else if (country === "India") {
      return "New Delhi";
    } else if (country === "Canada") {
      return "Ottawa";
    } else if (country === "Egypt") {
      return "Cairo";
    } else {
      return "";
    }
  }
}

class ProxyGetCapital {
  constructor() {
    this.capital = new GetCapital();
    this.cache = {};
  }
  getMycapital(country) {
    if (!this.cache[country]) {
      const value = this.capital.getMycapital(country);
      this.cache[country] = value;
      return `capital of ${country} is ${value}`;
    } else {
      return `capital of ${country} is ${this.cache[country]}`;
    }
  }
}

const capital = new ProxyGetCapital();
console.log(capital.getMycapital("Pakistan"));
console.log(capital.getMycapital("India"));
console.log(capital.getMycapital("Canada"));
console.log(capital.getMycapital("Egypt"));
console.log(capital.getMycapital("Egypt"));
console.log(capital.getMycapital("Egypt"));
console.log(capital.getMycapital("Pakistan"));
console.log(capital.getMycapital("Pakistan"));
console.log(capital.getMycapital("Canada"));