We can stop a property from being changed after it has initially been set by using the readonly keyword before the property name.

1. Let's give this a try on our Product interface by making the name property readonly:

interface Product {
  readonly name: string;
  unitPrice: number;
}

2. Let's also make sure we have an instance of the Product interface in place:

const table: Product = {
  name: "Table",
  unitPrice: 500
};

3. Let's change the name property table now on the next line:

table.name = "Better Table";

As expected, we get a compilation error:

readonly properties are a simple way of freezing their values after being initially set. A common use case is when you want to code in a functional way and prevent unexpected mutations to a property.