Proxy Pattern

The Proxy object in the design pattern can:

This enables to work through a Proxy object to perform additional functionality when accessing a subject. For example, to check the access rights of a client accessing a sensitive object.

Car Driver Example

In this example, we will create a class ProxyCar that will act as a proxy for the Car class by ensure that you of a correct age to drive the car (driveCar function).

This simple example can be replicated to help proxy things such as network requests or authentication to certain classes.

interface ICar {
  driveCar(): void;
}

// Real Object
class Car implements ICar {
  driveCar() {
    console.log('Car has been driven!');
  }
}

class ProxyCar implements ICar {
  private _driver: Driver;
  private _realCar: ICar;

  constructor(driver: Driver) {
    this._driver = driver;
    this._realCar = new Car();
  }

  driveCar() {
    if (this._driver.age < 16) {
      console.log('Driver is too young to drive');
    } else {
      this._realCar.driveCar();
    }
  }
}

class Driver {
  public age: number;

  constructor(age: number) {
    this.age = age;
  }
}

(function main() {
  const carWithIneligibleDriver: ICar = new ProxyCar(new Driver(15));
  carWithIneligibleDriver.driveCar(); // prints 'Driver is too young to drive'

  const carWithEligibleDriver: ICar = new ProxyCar(new Driver(25));
  carWithEligibleDriver.driveCar(); // prints 'Car has been driven'
})()
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