某个时间增加/减去N天之后的时间--JS方法

//date加上num天数之后等到的时间;date格式：YYYY-MM-DDfunction dateAddNumDays(date,num){var dates = date.split("-");if(dates.length!=3){alert("时间格式错误，请确认!");return ;}var year = dates[0];var month = dates[1];var day = dates[2];var newDay = Number(day)+Number(num);var oldDay = newDay;while(newDay>28){if(month==1||month==3||month==5||month==7||month==8||month==10||month==12){if(newDay>31){month = Number(month)+1;newDay = newDay-31;}}else if(month==4||month==6||month==9||month==11){if(newDay>30){month = Number(month)+1;newDay = newDay-30;}}else{if(isLeapYear(year)==true){if(newDay>29){month = Number(month)+1;newDay = newDay-29;}}else{if(newDay>28){month = Number(month)+1;newDay = newDay-28;}}}if(month>12){month = month-12;                        year = Number(year)+1;}if(oldDay == newDay){break;}}if(Number(month)<10){month = "0"+Number(month);}if(newDay<10){newDay = "0"+newDay;}return year+'-'+month+'-'+newDay;}//date减少num天数之后等到的时间;date格式：YYYY-MM-DDfunction dateReduceNumDays(date,num){var dates = date.split("-");if(dates.length!=3){alert("时间格式错误，请确认!");return ;}var year = dates[0];var month = dates[1];var day = dates[2];var newDay = Number(day)-Number(num);while(newDay<=0){if(month==1||month==2||month==4||month==6||month==8||month==9||month==11){newDay = newDay+31;month = Number(month)-1;}else if(month==5||month==7||month==10||month==12){newDay = newDay+30;month = Number(month)-1;}else{if(isLeapYear(year)==true){newDay = newDay+29;}else{newDay = newDay+28;}month = Number(month)-1;}if(month<=0){month = month+12;year = Number(year)-1;}}if(Number(month)<10){month = "0"+Number(month);}if(newDay<10){newDay = "0"+newDay;}return year+'-'+month+'-'+newDay;}//判断是否是闰年function isLeapYear(pYear){    if(!isNaN(pYear)){     if((pYear%4==0 && pYear%100!=0)||(pYear%100==0 && pYear%400==0)){     return true;     }else{     return false;     }    }else{    return false;    }}