Carousel iteration logic

Carousel iteration logic

// Items number
var items = elem.length;
// Any element containing data about current index
var current = elem.data('current');
var next;
// Button directory
var direction = elem.data('dir');

// Logic for calculating next items index
if (direction === 'next') {
    if (current === --items) {
        next = 0;
    } else {
        next = ++current;
    }
} else if (direction === 'prev') {
    if (current === 0) {
        next = --items;
    } else {
        next = --current;
    }
}

// Update element data about current index
elem.data('current', next);