Decorator Pattern example in TS

decorator.ts

interface IPrice {
    calculate(input: number): number;
}

class BasePrice implements IPrice {
    calculate(input: number): number {
        return input;
    }
}

abstract class PriceDecorator implements IPrice {

    protected price: IPrice;
    protected discountAmount: number;
    protected tax: number;
    
    constructor(price: IPrice) {
        this.price = price;
    }

    calculate(input: number): number {
        return this.price.calculate(input);
    }

}

class EmployeeDiscountDecorator extends PriceDecorator {
    discountAmount = 0.4;
    calculate(input: number): number {
        input = (input * (1 - this.discountAmount));
        return this.price.calculate(input);
    }
}

class PromoDiscountDecorator extends PriceDecorator {
    discountAmount = 0.1;
    calculate(input: number): number {
        input = (input * (1 - this.discountAmount));
        return this.price.calculate(input);
    }
}


class taxDecorator extends PriceDecorator {
    tax = 1.16;
    calculate(input: number): number {
        input = input * this.tax;
        return this.price.calculate(input);
    }
}  

const price = new BasePrice();
const employeeDiscount = new EmployeeDiscountDecorator(price);
// const promoDiscount = new PromoDiscountDecorator(employeeDiscount);
const taxedPrice = new taxDecorator(employeeDiscount)

console.log(taxedPrice.calculate(100));