用js进行日期与天数的加减

//用js进行日期与天数的加减  
function addDate(date, days) {
    if (days == undefined || days == '') {
        days = 1;
    }
    var d = new Date(date);
    d.setDate(d.getDate() + days);
    var m = d.getMonth() + 1;
    return d.getFullYear() + '-' + m + '-' + d.getDate();
}