README.md

Strategy

The Strategy pattern allows you to define a family of algorithms, encapsulate each one as a class, and make them interchangeable. This pattern lets the algorithm vary independently from the clients that use it.

// Strategy interface
class Strategy {
  execute(a, b) {
    throw new Error("This method should be overridden!");
  }
}

// Concrete strategies
class AddStrategy extends Strategy {
  execute(a, b) {
    return a + b;
  }
}

class SubtractStrategy extends Strategy {
  execute(a, b) {
    return a - b;
  }
}

class MultiplyStrategy extends Strategy {
  execute(a, b) {
    return a * b;
  }
}

class DivideStrategy extends Strategy {
  execute(a, b) {
    if (b === 0) {
      throw new Error("Division by zero!");
    }
    return a / b;
  }
}

// Context
class Calculator {
  constructor(strategy) {
    this.strategy = strategy;
  }

  setStrategy(strategy) {
    this.strategy = strategy;
  }

  executeStrategy(a, b) {
    return this.strategy.execute(a, b);
  }
}

Explaining the code

1. Strategy Interface: The Strategy class defines an interface with an execute method that must be overridden by concrete strategy classes.

2. Concrete Strategies: These classes extend the Strategy class and implement the execute method with specific algorithms.

3. Context: The Calculator class acts as the context that uses a Strategy object.

   • constructor(strategy): Initializes the calculator with a specific strategy.
   • setStrategy(strategy): Allows changing the strategy at runtime.
   • executeStrategy(a, b): Executes the current strategy's algorithm.

Usage

const calculator = new Calculator(new AddStrategy());
console.log(calculator.executeStrategy(5, 3)); // Output:

calculator.setStrategy(new SubtractStrategy());
console.log(calculator.executeStrategy(5, 3)); // Output: 2

calculator.setStrategy(new MultiplyStrategy());
console.log(calculator.executeStrategy(5, 3)); // Output: 15

calculator.setStrategy(new DivideStrategy());
console.log(calculator.executeStrategy(6, 3)); // Output: 2

Summary

The code implements the Strategy pattern to perform different arithmetic operations (addition, subtraction, multiplication, division) using interchangeable strategy objects. The Calculator class uses these strategies to execute the desired operation, allowing for flexible and dynamic changes to the algorithm used at runtime.