js 日期按年月日加减

<script>

function isleapyear(year)

{

    if(parseInt(year)%4==0 && parseInt(year)%100!=0)return true;

    if(parseInt(year)%400==0)return true;

    return false;

}



function datedrift(date,difference)

{    

    if(date.constructor!==Date)return Date();

    var year=parseInt(date.getUTCFullYear()),

        mon=parseInt(date.getUTCMonth())+1,

        day=parseInt(date.getUTCDate());

    if(typeof difference!="string" || difference.length==0)return date;

    var units=difference.match(/([+-]\d{1,3}[myd])/ig);

    for(var i=0;i<units.length;i++)

    {

        if(units[i].charAt(0)=='+')

        {

            var mark=units[i].substr(-1,1);

            var value=parseInt(units[i].substr(1,units[i].length-2));

            if(mark =='y')

            {

                year=year+value;

                if(day==29)

                {

                    year=year+value;

                    if(mon==2)

                    {

                        if(!isleapyear(year))

                            day=28;

                    }

                }

            }

            else if(mark == 'm')

            {

                year+=Math.floor((value+mon-1)/12);

                mon=(value+mon-1)%12+1;

                if(day==29 && mon==2 && !isleapyear(year))day=28;

                else if(day>=30 && mon==2)

                {

                    if(isleapyear(year))day=29;

                    else day=28;

                }

                else if(day==31 && (mon==4 || mon==6 || mon==9 || mon==11))day=30;

            }

            else if(mark== 'd')

            {

                var tmp=new Date();

                tmp.setTime(Date.parse(year+'-'+mon+'-'+day)+value*24*36e5);

                year=tmp.getUTCFullYear();

                mon=tmp.getUTCMonth()+1;

                day=tmp.getUTCDate();

            }



        }

        else

        {

            var mark=units[i].substr(-1,1);

            var value=parseInt(units[i].substr(1,units[i].length-2));

            switch(mark)

            {

                case "y":

                    year-=value;

                    if(day==29)

                    {

                        if(mon==2)

                        {

                            if(!isleapyear(year))

                                day=28;

                        }

                    }

                break;

                case "m":

                    var minusyear=Math.floor(value/12);

                    if(value%12>0)

                    {

                        year=year-minusyear-1;

                        year+=Math.floor((mon+11-value%12)/12);

                        mon=(mon+11-(value%12))%12+1;



                        

                        if(day==29 && mon==2 && !isleapyear(year))day=28;

                        else if(day>=30 && mon==2)

                        {

                            if(isleapyear(year))day=29;

                            else day=28;

                        }

                        else if(day==31 && (mon==4 || mon==6 || mon==9 || mon==11))day=30;

                    }

                    else

                    {

                        year=year-minusyear;

                        if(day==29 && mon==2 && !isleapyear(year))day=28;

                        else if(day>=30 && mon==2)

                        {

                            if(isleapyear(year))day=29;

                            else day=28;

                        }

                        else if(day==31 && (mon==4 || mon==6 || mon==9 || mon==11))day=30;

                    }

                break;

                case "d":

                    var tmp=new Date();

                    tmp.setTime(Date.parse(year+'-'+mon+'-'+day)-value*24*36e5);

                    year=tmp.getUTCFullYear();

                    mon=tmp.getUTCMonth()+1;

                    day=tmp.getUTCDate();

                break;

            }

        }

    }

    alert([year,mon,day]);

}

var curdate=new Date();

datedrift(curdate,"+5m -5m");

</script>