JS Implementation Control Date Month increase or decrease

Define a current date variable

var mydate = new Date ();

Process Month Add function (date current date, num increment month "positive number: Add month, Negative: Decrease month")
function addmonth (date, num) {
    num = parseint (num);
    var sdate = datetodate (date);

    var syear = Sdate.getfullyear ();
    var smonth = sdate.getmonth () + 1;
    var sday = Sdate.getdate ();

    var eyear = syear;
    var emonth = smonth + num;
    var eday = sday;
    while (Emonth >) {
      eyear++;
      Emonth-= 12;
   }

    var eDate = new Date (eyear, eMonth-1, eday);

    while (Edate.getmonth ()! = eMonth-1) {
      eday--;
      eDate = new Date (eyear, eMonth-1, Eday);
   }

    return eDate;
};

function Datetodate (date) {
var sdate = new Date ();
if (typeof date = = ' object '
&& typeof New Date (). GetMonth = = "function"
) {
Sdate = date;
}
else if (typeof date = = "string") {
var arr = date.split ('-')
if (arr.length = = 3) {
Sdate = new Date (arr[0] + '-' + arr[1] + '-' + arr[2]);
}
}

return sdate;
}；

Formatting date functions

Date.prototype.Format = function (FMT)
{//author:meizz
var o = {
"m+": This.getmonth () +1,//month
"D+": this.getdate (),//day
"H +": this.gethours (),//hour
"m+": this.getminutes (),//min
"S+": This.getseconds (),//sec
"q+": Math.floor ((This.getmonth () +3)/3),//Quarterly
"S": this.getmilliseconds ()//MS
};
if (/(y+)/.test (FMT))
Fmt=fmt.replace (Regexp.$1, (this.getfullyear () + ""). substr (4-regexp.$1.length));
For (var k in O)
if (New RegExp ("(" + K + ")"). Test (FMT))
FMT = Fmt.replace (regexp.$1, (regexp.$1.length==1)? (O[k]): (("XX" + o[k]). substr (("" + O[k]).));
return FMT;
};

Calling functions

var mydate = new Date ();
Alert (Addmonth (mydate, 1). Format ("Yyyy-mm-dd"));

Execution effect

JS Implementation Control Date Month increase or decrease