Adapter

Wraps an existing class in a new interface so it can work with code that expects a different interface. Acts as a translator between two incompatible interfaces.

When to Use

• Integrating a third-party library with an incompatible interface
• Reusing existing classes that can't be modified
• Multiple classes with similar behaviour but different interfaces must be used uniformly
• Gradual migration between old and new interfaces

How to Apply

1. Define the Target interface that clients expect
2. Identify the Adaptee class with the incompatible interface
3. Create an Adapter class that implements Target and holds a reference to Adaptee
4. Implement each Target method by translating the call to the appropriate Adaptee method
5. Clients use the Adapter via the Target interface

Example

// Existing (Adaptee) — uses XML
class XmlAnalytics {
  analyzeXml(xml: string): object { return {}; /* parse xml */ }
}

// Target interface clients expect
interface Analytics {
  analyze(data: object): object;
}

// Adapter
class AnalyticsAdapter implements Analytics {
  constructor(private adaptee: XmlAnalytics) {}
  analyze(data: object): object {
    const xml = JSON.stringify(data); // convert to xml format
    return this.adaptee.analyzeXml(xml);
  }
}

// Client code
const analytics: Analytics = new AnalyticsAdapter(new XmlAnalytics());
analytics.analyze({ users: 42 });

References

• refactoring.guru/design-patterns/adapter