CODESAMPLE

Adapter - JavaScript

Adapter JavaScript

The Adapter pattern converts the interface of a class into another interface clients expect. It lets classes work together that couldn’t otherwise because of incompatible interfaces. This example demonstrates adapting a legacy logging service (with a log() method accepting a single string) to a modern logging interface (an AdapterLogger requiring objects with level and message properties). The LegacyLoggerAdapter handles this conversion, allowing modern clients to use the old service without modification. This fits JavaScript’s flexible object nature, leveraging objects as configuration to adapt behavior.

// Legacy Logging Service: Incompatible interface
class LegacyLogger {
  log(message) {
    console.log(`LEGACY: ${message}`);
  }
}

// Modern Logging Interface: What clients expect
class AdapterLogger {
  log(logObject) {
    if (!logObject || !logObject.level || !logObject.message) {
      console.error("Invalid log object. Expected { level: '...', message: '...' }");
      return;
    }
    console.log(`ADAPTER: [${logObject.level}] ${logObject.message}`);
  }
}

// Adapter: Converts LegacyLogger's interface to AdapterLogger
class LegacyLoggerAdapter {
  constructor(legacyLogger) {
    this.legacyLogger = legacyLogger;
  }

  log(logObject) {
    if (!logObject || !logObject.message) {
      console.error("Invalid log object. Expected { message: '...' }");
      return;
    }
    this.legacyLogger.log(logObject.message);
  }
}

// Client Code: Uses the AdapterLogger interface
function clientCode(logger) {
  logger.log({ level: 'INFO', message: 'This is an informational message.' });
  logger.log({ level: 'WARNING', message: 'Something needs attention.' });
  logger.log({ message: 'Error from client code' });  //Will trigger error handling.
}

// Usage:
const legacyLogger = new LegacyLogger();
const adapter = new LegacyLoggerAdapter(legacyLogger);
const modernLogger = new AdapterLogger();

clientCode(adapter);
clientCode(modernLogger);