src/decorator/index.ts

// https://en.wikipedia.org/wiki/Decorator_pattern

namespace DecoratorPattern {
  interface Component {
    operation(): void;
  }

  class ConcreteComponent implements Component {
    private s: String;

    constructor(s: String) {
      this.s = s;
    }

    public operation(): void {
      console.log(
        "`operation` of ConcreteComponent",
        this.s,
        " is being called!"
      );
    }
  }

  class Decorator implements Component {
    private component: Component;
    private id: Number;

    constructor(id: Number, component: Component) {
      this.id = id;
      this.component = component;
    }

    public get Id(): Number {
      return this.id;
    }

    public operation(): void {
      console.log("`operation` of Decorator", this.id, " is being called!");
      this.component.operation();
    }
  }

  class ConcreteDecorator extends Decorator {
    constructor(id: Number, component: Component) {
      super(id, component);
    }

    public operation(): void {
      super.operation();
      console.log(
        "`operation` of ConcreteDecorator",
        this.Id,
        " is being called!"
      );
    }
  }

  // Client code
  var decorator1 = new ConcreteDecorator(1, new ConcreteComponent("Comp1"));
  decorator1.operation();

  // Output
  /*
    `operation` of Decorator 1  is being called!
    `operation` of ConcreteComponent Comp1  is being called!
    `operation` of ConcreteDecorator 1  is being called!
  */
}