Optional Properties

An object can specify Optional Properties by adding a question mark ? to the end of the property name:

type X = {
    a: number;
    b?: number; // Optional
};

It is possible to specify a default value when a property is optional:

type X = {
    a: number;
    b?: number;
};
const x = ({ a, b = 100 }: X) => a + b;