README.md

STRATEGY PATTERN

Defines a family of algorithms, encapsulates each one, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it.

When to use the strategy pattern?

• When you want to define a class that will have one behavior that is similar to other behaviors in a list
• When you need to use one of several behaviors dynamically
• When you want to change the behavior of an object at runtime

Strategy Pattern UML Diagram

Example

interface Strategy {
  execute(a: number, b: number): number;
}

class Add implements Strategy {
  execute(a: number, b: number): number {
    return a + b;
  }
}

class Subtract implements Strategy {
  execute(a: number, b: number): number {
    return a - b;
  }
}

class Multiply implements Strategy {
  execute(a: number, b: number): number {
    return a * b;
  }
}

class Context {
  private strategy: Strategy;

  constructor(strategy: Strategy) {
    this.strategy = strategy;
  }

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

const context = new Context(new Add());
console.log("Add: " + context.executeStrategy(10, 5));

context = new Context(new Subtract());

console.log("Subtract: " + context.executeStrategy(10, 5));

context = new Context(new Multiply());

console.log("Multiply: " + context.executeStrategy(10, 5));

Output

Add: 15
Subtract: 5
Multiply: 50

Resources

• https://en.wikipedia.org/wiki/Strategy_pattern
• https://refactoring.guru/design-patterns/strategy
• https://www.dofactory.com/javascript/design-patterns/strategy
• https://www.geeksforgeeks.org/strategy-pattern-set-1/

Implementation

• Define a strategy interface with a method that will be implemented by concrete strategies
• Implement concrete strategies that implement the strategy interface
• Define a context class that will use the strategy
• In the context class, add a method that will set the strategy
• In the context class, add a method that will execute the strategy
• Create an instance of the context class and pass a concrete strategy to it
• Call the method that will execute the strategy

For more code snippets, check the code in the src folder.

To run the main file (src/index.ts) and see the output, run ts-node src/index.ts in your terminal.

N/B: You must have ts-node installed globally to run the command above. If you don't have it installed, you can install it by running npm install -g ts-node.