获取当前日期，例为：2017-07-28

var day=0;
var month=0;
var year=0;
var today="";
mydate=new Date();
mymonth=mydate.getMonth()+1;
myday= mydate.getDate();
myyear= mydate.getFullYear();
year=(myyear > 200) ? myyear : 1900 + myyear;

if(mymonth >= 10){mymonth=mymonth;}else{mymonth="0" + mymonth;}
if(myday >= 10){myday=myday;}else{myday="0" + myday;}

today=year+'-'+mymonth+'-'+myday;//2017-09-05；

//去除<=10的月份、日期前的0；

if(mymonth <= 10){

mymonth = mymonth.replace('0','')

}else{

mymonth= mymonth;
}

if(myday <= 10){

myday = myday.replace('0','')

}else{

myday= myday;
}

//获取当前年月 
var date=new Date;
var year=date.getFullYear();
var month=date.getMonth()+1;
month =(month<10 ? "0"+month:month);//加0
var mydate = (year.toString()+'-'+month.toString());

//获取当前日期
function getDay(day){
　　var today = new Date(); 
　　var targetday_milliseconds=today.getTime() + 1000*60*60*24*day; 
　　today.setTime(targetday_milliseconds); //注意，这行是关键代码 
　　var tYear = today.getFullYear(); 
　　var tMonth = today.getMonth(); 
　　var tDate = today.getDate(); 
　　tMonth = doHandleMonth(tMonth + 1); 
　　tDate = doHandleMonth(tDate); 
　　return tYear+"-"+tMonth+"-"+tDate; 
}

//日期拼接
function doHandleMonth(month){
　　var m = month; 
　　if(month.toString().length == 1){ 
　　　　m = "0" + month; 
　　} 
　　return m; 
}

var Yesterday = getDay(-1),Today = getDay(0),Last3days = getDay(-2)+','+getDay(0),Last7days = getDay(-6)+','+getDay(0); //取值