max(selector?): PartialLens

ts
max: <A extends number>() => PartialLens<A, A[]>;
max: <A>(selector?: (a: A) => number) => PartialLens<A, A[]>;

ts
max: <A extends number>() => PartialLens<A, A[]>;
max: <A>(selector?: (a: A) => number) => PartialLens<A, A[]>;

---

This combinator, when passed to derive, returns an optic focused on the highest number from the focused array.

ts
import { max } from "@optics/react/combinators";
 
const maxOptic = createState([42, 16, 98, 123, 8]).derive(max());
 
maxOptic.get(); // 123
 
maxOptic.set(97);
 
maxOptic.get(); // 98

ts
import { max } from "@optics/react/combinators";
 
const maxOptic = createState([42, 16, 98, 123, 8]).derive(max());
 
maxOptic.get(); // 123
 
maxOptic.set(97);
 
maxOptic.get(); // 98

Here 123 is the max element, and when we set it to 97 then the element at index 2 (98) becomes the max element.

Selector

If the elements in the focused array aren't numbers, then you must pass a selector to get a number from each element in the array:

ts
import { max } from "@optics/react/combinators";
 
const usersOptic = createState([
  { name: "Jack", age: 23 },
  { name: "Jeanne", age: 56 },
]);
 
const oldestUserOptic = usersOptic.derive(max((user) => user.age));
 
oldestUserOptic.get(); // { name: "Jeanne", age: 56 }
 
usersOptic[0].age.set(80);
 
oldestUserOptic.get(); // { name: "Jack", age: 80 }

ts
import { max } from "@optics/react/combinators";
 
const usersOptic = createState([
  { name: "Jack", age: 23 },
  { name: "Jeanne", age: 56 },
]);
 
const oldestUserOptic = usersOptic.derive(max((user) => user.age));
 
oldestUserOptic.get(); // { name: "Jeanne", age: 56 }
 
usersOptic[0].age.set(80);
 
oldestUserOptic.get(); // { name: "Jack", age: 80 }