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Facade

Overview​

Provide a simplified interface to a complex subsystem.

When to use​

  • You want a clean API for a complex set of classes.
  • You want to decouple clients from subsystem details.

Java example​

class PaymentFacade {
    private final FraudCheck fraud = new FraudCheck();
    private final PaymentGateway gateway = new PaymentGateway();

    public boolean pay(String userId, int amount) {
        if (!fraud.isAllowed(userId, amount)) {
            return false;
        }
        return gateway.charge(userId, amount);
    }
}

TypeScript example​

class PaymentFacade {
  private fraud = new FraudCheck();
  private gateway = new PaymentGateway();

  pay(userId: string, amount: number): boolean {
    if (!this.fraud.isAllowed(userId, amount)) {
      return false;
    }
    return this.gateway.charge(userId, amount);
  }
}

Pros and cons​

Pros:

  • Simplifies client usage.
  • Reduces coupling.

Cons:

  • Can become a god object.
  • May hide important capabilities.

Common pitfalls​

  • Putting business logic into the facade.
  • Growing the facade instead of creating focused APIs.