README.md

Template Method Pattern

The Template Method pattern locks down the structure of an algorithm in a base class but lets subclasses fill in the specific steps. The "template" is the fixed sequence; the blanks are what change between implementations.

Example

class DataProcessor {
  process() {
    this.loadData();
    this.processData();
    this.saveData();
  }

  loadData() {
    throw new Error("You have to implement the method loadData!");
  }

  processData() {
    throw new Error("You have to implement the method processData!");
  }

  saveData() {
    throw new Error("You have to implement the method saveData!");
  }
}

class CSVDataProcessor extends DataProcessor {
  loadData() {
    console.log("Loading data from CSV file");
    // Load CSV data
  }

  processData() {
    console.log("Processing CSV data");
    // Process CSV data
  }

  saveData() {
    console.log("Saving processed data to CSV file");
    // Save processed data
  }
}

class JSONDataProcessor extends DataProcessor {
  loadData() {
    console.log("Loading data from JSON file");
    // Load JSON data
  }

  processData() {
    console.log("Processing JSON data");
    // Process JSON data
  }

  saveData() {
    console.log("Saving processed data to JSON file");
    // Save processed data
  }
}

Explaining the code

1. Base Class: DataProcessor

   • The DataProcessor class contains a method process() which outlines the steps for processing data: loadData(), processData(), and saveData().
   • Each of these methods (loadData(), processData(), and saveData()) throws an error, indicating that they must be implemented by subclasses.

2. Subclass: CSVDataProcessor

   • Inherits from DataProcessor.
   • Implements the loadData(), processData(), and saveData() methods specifically for CSV data.
   • Each method logs a message to the console indicating its operation.

3. Subclass: JSONDataProcessor

   • Inherits from DataProcessor.
   • Implements the loadData(), processData(), and saveData() methods specifically for JSON data.
   • Each method logs a message to the console indicating its operation.

Usage

const csvProcessor = new CSVDataProcessor();
csvProcessor.process();

const jsonProcessor = new JSONDataProcessor();
jsonProcessor.process();

• Instances of CSVDataProcessor and JSONDataProcessor are created.
• The process() method is called on each instance, which in turn calls the overridden methods (loadData(), processData(), and saveData()) in the respective subclasses.

Summary

process() always runs loadData → processData → saveData in that order: the sequence is guaranteed by the base class. Subclasses only care about their specific steps, not the overall flow. It's a simple way to enforce a pipeline without duplicating the orchestration logic in every implementation.