To get the previous and next elements of an array loop in JavaScript, we use the modulo operator.

For instance, we write

const len = array.length;

const current = array[i];
const previous = array[(i + len - 1) % len];
const next = array[(i + 1) % len];

to get the current array item with index i.

We get the previous item’s index with (i + len - 1) % len.

And we get the next item with index (i + 1) % len.