jquery獲取指定日期后一個月的日期及天數

//指定日期一月的天數
function maxDay() {
    //字符串日期格式"2020-12-12"
    var sDate = $('#startDate').val();
    //轉換為日期
    var startDate = new Date(sDate)
    var endDate = startDate.setMonth(startDate.getMonth()+1);
    endDate = formatDate(endDate);
    var days =  daysBetween(sDate,endDate);
    return days;
}
//指定日期獲取一個月
function formatDate(date) {
    var date = new Date(date);
    var YY = date.getFullYear() + '-';
    var MM = (date.getMonth() + 1 < 10 ? '0' + (date.getMonth() + 1) : date.getMonth() + 1) + '-';
    var DD = (date.getDate() < 10 ? '0' + (date.getDate()) : date.getDate());
    return YY + MM + DD;
}
//計算兩日期天數
function daysBetween(sDate1,sDate2){
    var time1 = Date.parse(new Date(sDate1));
    var time2 = Date.parse(new Date(sDate2));
    var nDays = Math.abs(parseInt((time2 - time1)/1000/3600/24));
    return nDays;
};