Learn React with TypeScript 3

Method signatures

Interfaces can contain method signatures as well. These won't contain the implementation of the method; they define the contracts for when interfaces are used in an implementation.

Let's look at an example:

1. Let's add a method to the OrderDetail interface we just created. Our method is called getTotal and it has a discount parameter of type number and returns a number:

interface OrderDetail {  product: Product;   quantity: number;  getTotal(discount: number): number; }

Notice that the getTotal method on the interface doesn't specify anything about how the total is calculated – it just specifies the method signature that should be used.

2. Having adjusted our OrderDetail interface, our tableOrder object, which implemented this ...