How can I use union types with interfaces in TypeScript?

How can I use union types with interfaces in TypeScript?

You can use union types with interfaces to define a variable that can hold multiple types. For example, you can create an interface for a shape and use a union type to specify that a variable can be either a Circle or a Rectangle.

Can you show me an example of that?

Sure! Here's a simple example:

interface Circle {
    radius: number;
}

interface Rectangle {
    width: number;
    height: number;
}

type Shape = Circle | Rectangle;

function getArea(shape: Shape): number {
    if ('radius' in shape) {
        return Math.PI * shape.radius ** 2;
    } else {
        return shape.width * shape.height;
    }
}

This function calculates the area based on the type of shape.

What if I want to add another shape later?

You can easily extend the union type by adding another interface for the new shape. Just update the Shape type to include the new interface.

Thanks! This is really helpful.