[Vlasenko Fedor]

function next(items) {
    var max = items.length - 1,
        i = -1;
    return function () {
        i = i < max ? i + 1 : 0;
        return items[i];
    };
}

var imagName = next(['p01', 'p02', 'p03']);
alert('upload/' + imagName() + '.jpg');
alert('upload/' + imagName() + '.jpg');
alert('upload/' + imagName() + '.jpg');
alert('upload/' + imagName() + '.jpg');