Logical algorithm for previous and next items
This can be used on pictures, news, shop items, etc. with JavaScript events for “previous” and “next”
if (prev === null) {
prev = current && next = current + 1
} elseif (next === null) {
next = current && prev = current -1
} else {
if (action == prev) {
next = current
prev = current - 1
} elseif (action == next) {
prev = current
next = current + 1
} else {
prev = current - 1
next = current + 1
}
}