Behavioral Design Patterns

Strategy Design Pattern (Behavioral) §

Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm exist very independently from clients that use it.

 
/**
 * The Context defines the interface of interest to clients.
 */
class Context {
 
    private strategy: Strategy;
 
    constructor(strategy: Strategy) {
        this.strategy = strategy;
    }
 
    public setStrategy(strategy: Strategy) {
        this.strategy = strategy;
    }
 
    public doSomeBusinessLogic(): void {
        console.log('Context: Sorting data using the strategy (not sure how it\'ll do it)');
        const result = this.strategy.doAlgorithm(['a', 'b', 'c', 'd', 'e']);
        console.log(result.join(','));
    }
}
 
interface Strategy {
    doAlgorithm(data: string[]): string[];
}
 
class ConcreteStrategyA implements Strategy {
    public doAlgorithm(data: string[]): string[] {
        return data.sort();
    }
}
 
class ConcreteStrategyB implements Strategy {
    public doAlgorithm(data: string[]): string[] {
        return data.reverse();
    }
}
 
const context = new Context(new ConcreteStrategyA());
console.log('Client: Strategy is set to normal sorting.');
context.doSomeBusinessLogic();
 
console.log('');
 
console.log('Client: Strategy is set to reverse sorting.');
context.setStrategy(new ConcreteStrategyB());
context.doSomeBusinessLogic();