Learn React with TypeScript 3

Optional properties and parameters

We might want to make a property optional because not every situation where the interface is implemented requires it. Let's take the following steps in our OrderDetail interface:

1. Let's create an optional property for the date it was added. We specify an optional value by putting a ? at the end of the property name but before the type annotation:

interface OrderDetail {  product: Product;  quantity: number;  dateAdded?: Date,  getTotal(discount: number): number;}

We'll see that our implementation of this interface, tableOrder, isn't broken. We can choose to add dateAdded to tableOrder but it isn't required.

2. We might also want to make a method parameter optional. We do this in a similar way by putting a ?