var firstDay = '2015-03-26';
var allDays = 6;

function makeRequestDate(start, d) {
    var date = new Date(start);
    date.setDate(date.getDate() + d);
    var newDate = date.toISOString().split('T');
    return newDate[0];
}

for (var i = 0; i < allDays; i++) {
                var date = makeRequestDate(firstDay, i);
                console.log(date);
              
}

wynik

2015-03-26
2015-03-27
2015-03-28
2015-03-29
2015-03-29??
2015-03-30??

function makeRequestDate(start, d) {
    var date = new Date(start);
    date.setDate(date.getDate() + d);
    var newDate = date.toISOString().split('T');
    if (newDate[1] == '23:00:00.000Z') {
        date.setDate(date.getDate() + 1);
        newDate = date.toISOString().split('T');
    }
    return newDate[0];
}