how do you add a property to an existing type in typescript?

July 31, 2023 by Tarik

In typescript, If you want to add members, you can use an intersection type:

type DateWithNewMember <T> = Partial<T>
   & { newMember: boolean }

Then use like this:

dates: DateWithNewMember<Date>[];

You could use Union type:

class newDateClass {
   readonly fullYearUTC: number;
}

Then use like this:

date: Date | newDateClass