at(index): Lens

ts
at: <A>(index: number) => Lens<A, A[]>;

ts
at: <A>(index: number) => Lens<A, A[]>;

---

This combinator takes an index and, when passed to derive, returns an optic focused on the element at the index in the focused array.
Just like JavaScript's Array.at, a negative index counts back from the end of the array.

ts
import { at } from "@optics/react/combinators";
 
const numbersOptic = createState([78, 90, 4, 7, 10, 789, 42, 90]);
 
const fifthElementOptic = numbersOptic.derive(at(4));
             
const fifthElementOptic: Optic<number, partial>
fifthElementOptic.get(); // 10
 
numbersOptic.derive(at(-2)).get(); // 42

ts
import { at } from "@optics/react/combinators";
 
const numbersOptic = createState([78, 90, 4, 7, 10, 789, 42, 90]);
 
const fifthElementOptic = numbersOptic.derive(at(4));
             
const fifthElementOptic: Optic<number, partial>
fifthElementOptic.get(); // 10
 
numbersOptic.derive(at(-2)).get(); // 42