javascript以当前日期为准计算当月、上月、下月直接输出日期的解决方案

//获取当月;
function getMonths(mons, today) {
    var d = new Date();
    var nowYear = d.getFullYear().toString();//今年
    var nowMonth = timeAdd0((d.getMonth() + 1 + Number(mons)).toString());//当月
    var nowDay = timeAdd0(d.getDate().toString());//当日
    if (today == "0") {
        var now = nowYear + "-" + nowMonth + "-" + nowDay;//今日标准时间; 2020-09-02
    } else {
        var now = nowYear + "-" + nowMonth + "-" + "01";//今日标准时间; 2020-09-02
    }
    return now;
}
//补齐十位数;
function timeAdd0(str) {
    if (str.length <= 1) {
        str = '0' + str;
    }
    return str
}