What I call “wraparound” are repeatable indices on an array. The common use case is a carousel. Here’s how it’s done:

const items = ["first", "middle", "last"];
const i = 0; // Our iterable index

// "Next" ->
const nextIndex = (i + 1) % items.length;

// <- "Previous"
const prevIndex = (i - 1 + items.length) % items.length;