A common pattern, especially when dealing with collections of data (read: arrays), is to have a function that can transform an array of any type of data. In order to keep this kind of function general-purpose and have it preserve types, we'll need to use generics.
For an anonymous function to work with a generic type, it needs to open with a signature for the generic type:
<T>() => {}With that in mind, we can write a function that accepts an array of type T,
does something to that collection, and then returns an array of type T.
For instance, here is a function that takes the first n elements from the
array and returns them.
const take = <T>(arr: Array<T>, n: number): Array<T> => {
return arr.slice(0, n)
}This both enforces and preserves the type of the array. It works well for situations where the array is a bunch of complex objects with specific types like we'd get from a Prisma query.