Mark Object Property As Optional in TypeScript

In TypeScript, you can mark an object property as optional by using a question mark ? after the property name. This indicates that the property is not required and can be omitted when creating or using objects that have this property.

Here's an example:

interface Person {
  name: string;
  age?: number;
}

const person1: Person = {
  name: "Alice",
  age: 30,
};

const person2: Person = {
  name: "Bob",
};

In this example, the Person interface has an optional age property marked with a question mark. The person1 object includes the age property, while the person2 object omits it.

Note that when accessing an optional property, you should check whether it exists first to avoid runtime errors. You can use the in operator or the typeof operator to check for the existence of an optional property. For example:

if ("age" in person1) {
  console.log(person1.age);
}

if (typeof person2.age === "number") {
  console.log(person2.age);
}