Importing allows us to import items from an exported module. We do this using an import statement that includes the item names to import in curly braces and the file path to get the items from (excluding the ts extension). We can only import items that are exported in the other module file.

1. Let's resolve the issue with our OrderDetail class by importing the Product interface:

import { Product } from "./product";

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

2. We can rename imported items using the as keyword in an import statement. We then reference the item in our code using the new name:

import { Product as Stock } from "./product";

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