TS4117

This member cannot have an 'override' modifier because it is not declared in the base class.

Broken Code ❌

class Strategy {
  processCandle(candle: number): void {
    console.log('Processing candle:', candle);
  }
}
 
class TradingStrategy extends Strategy {
  override processCandel(candle: number): void {
    console.log('Trading with candle:', candle);
  }
}

Fixed Code ✔️

class Strategy {
  processCandle(candle: number): void {
    console.log('Processing candle:', candle);
  }
}
 
class TradingStrategy extends Strategy {
  override processCandle(candle: number): void {
    console.log('Trading with candle:', candle);
  }
}

The override modifier can only be used on methods that actually exist in the base class. In this case, processCandel was misspelled. It should be processCandle to match the base class method name.