A lens is a functional way to focus on a specific part of a data structure. It is similar to a getter and setter, but it is immutable.
import { Lens } from 'minifunc';
const lens = Lens('Name of the field you want to target');
AnythingWith is extremely useful for type safety. It is used to make sure that the field you’re targeting is actually in the object you’re targeting.get and maybeGet is exactly the same. The only difference is in types, where get will make your build fail if you’re passing an object that doesn’t have the field you’re targeting.set and change. set doesn’t require the field to already exist, while change does.Lens<T, U>type AnythingWith<Field extends string | number | symbol, T> = {
[_ in Field]: T;
};
interface Lens<T extends string | number | symbol, I> {
get<U extends AnythingWith<T, I>>(obj: U): I;
maybeGet<U>(obj: U): I | undefined;
set<U>(obj: U, value: I): U;
change<U extends AnythingWith<T, I>, I>(obj: U, value: I): U;
map<U extends AnythingWith<T, I>, J>(obj: U, f: (old: I) => J): U;
}