Just a reference to go back and forth into an array with loop. See it in action: http://run.plnkr.co/plunks/7ngbHx/

Back 'n Forth

var step = 1,
    active = 0,
    items = new Array();

function next(){
	active = (active + step) % items.length;
	// active = ++active % items.length;
}
 
function prev(){
	active = (active - step) % items.length;
	if ( active < 0 ) active = items.length - Math.abs(active);
	// simple for 1 step
	// active = active ? --active : items.length - Math.abs(--active);
}