function Test(day) {
var today = new Date();
var beforMilliseconds = today.getTime() - 1000 * 3600 * 24 * day;
var beforday = new Date();
beforday.setTime(beforMilliseconds);
var strYear = beforday.getFullYear();
var strDay = beforday.getDate();
var strMonth = beforday.getMonth() + 1;
if (strMonth < 10) {
strMonth = "0" + strMonth;
}
var strYesterday = strYear + "-" + strMonth + "-" + strDay;
alert(strYesterday);
}