Static

Static properties and methods are held in the class itself and not in class instances. They can be declared using the static keyword before the property or method name.

Let's look at the following example:

1. Let's make the getTotal method static on the OrderDetail class we have been using:

class OrderDetail {
  product: Product;
  quantity: number;

  static getTotal(discount: number): number {
    const priceWithoutDiscount = this.product.unitPrice * this.quantity;
    const discountAmount = priceWithoutDiscount * discount;
    return priceWithoutDiscount - discountAmount;
  }
}

1. We get compilation errors where we try to reference the properties on the class. This is because the static method isn't in the class instance and therefore can't access these properties:

1. To make the static method work, we can move its dependencies on the class instance to parameters in the function:

static getTotal(unitPrice: number, quantity: number, discount: number): number {
  const priceWithoutDiscount = unitPrice * quantity;
  const discountAmount = priceWithoutDiscount * discount;
  return priceWithoutDiscount - discountAmount;
}

1. We can now call the static method on the class type itself, passing in all the parameter values:

const total = OrderDetail.getTotal(500, 2, 0.1);
console.log(total);

If we run the preceding program, we should get an output of 900 in the console.