How `satisfies` works

type ColorWithId = {
     id: string
     color?: string
}

// Declaring myColor1, supplying ColorWithId type
const myColor1: ColorWithId = { id: 'a', color: 'red' }

myColor.id.substring(0, 1) // ok

myColor.color.substring(0, 1) // TypeError: 'myColor1.color' is possibly 'undefined'.

To fix this, we need to apply optional chaining: myColor1.color?.sub... But this doesn't make sense because it's obvious that there is a color property with the value 'red'!

How about casting?

const myColor = { id: 'a', color: 'red' } as ColorWithId

myColor.color.substring(0, 1) // TypeError: 'myColor1.color' is possibly 'undefined'.

The same as above of course.

How about using satisfies?

const myColor = { id: 'a', color: 'red' } satisfies ColorWithId

myColor.color.substring(0, 1) // ok

There's no TypeError. Because the value "satisfies" the type.

Does satisfies still check the type correctly??

const myColor = { id: 'a', colors: 'red' } satisfies ColorWithId
//                             ^ TypeError: 'colors' does not exist in type 'ColorWithId'

Yes, it does.