SOLID Principles in JavaScript

Which SOLID principle is being applied in this payment processing implementation?

interface PaymentStrategy {
  process(amount: number): Promise<void>;
}

class CreditCardPayment implements PaymentStrategy {
  process(amount: number) { /* ... */ }
}

class PayPalPayment implements PaymentStrategy {
  process(amount: number) { /* ... */ }
}

class CryptoPayment implements PaymentStrategy {
  process(amount: number) { /* ... */ }
}

class PaymentProcessor {
  constructor(private strategy: PaymentStrategy) {}

  processPayment(amount: number) {
    return this.strategy.process(amount);
  }
}

Interface Segregation Principle
Single Responsibility Principle
Open/Closed Principle
This code demonstrates the Open/Closed Principle (OCP). The PaymentProcessor class is closed for modification but open for extension through the PaymentStrategy interface. New payment methods can be added by creating new classes that implement the PaymentStrategy interface, without modifying existing code. This design also shows the Strategy pattern, which is a common way to implement OCP.
Dependency Inversion Principle

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