javascript获取当前，近7天，近1个月，近3个月的日期

var date=new Date();
var year=date.getFullYear();
var month=date.getMonth()+1>10?date.getMonth()+1:'0'+date.getMonth()+1;
var day=date.getDate()>10?date.getDate():'0'+date.getDate();
var nowdatestr=year+"-"+month+"-"+day;

//今天
$("#today").click(function(){
$("#begin_time").val(nowdatestr);
});
//近7天
$("#sevenday").click(function(){
var oneweekdate=new Date(date-6*24*3600*1000);
var year1=oneweekdate.getFullYear();
var month1=oneweekdate.getMonth()+1>10?oneweekdate.getMonth()+1:'0'+oneweekdate.getMonth()+1;
var day1=oneweekdate.getDate()>10?oneweekdate.getDate():'0'+oneweekdate.getDate();
$("#begin_time").val(year1+"-"+month1+"-"+day1);
});
//近1个月
$("#onemonth").click(function(){
$("#begin_time").val(getPreMonthDay(nowdatestr,1));
});
//近3个月
$("#threemonth").click(function(){
$("#begin_time").val(getPreMonthDay(nowdatestr,3));
});
//获取当前日期前N个月的日期
function getPreMonthDay(date,monthNum)
{
var dateArr = date.split('-');
var year = dateArr[0]; //获取当前日期的年份
var month = dateArr[1]; //获取当前日期的月份
var day = dateArr[2]; //获取当前日期的日
var days = new Date(year, month, 0);
days = days.getDate(); //获取当前日期中月的天数
var year2 = year;
var month2 = parseInt(month) - monthNum;
if (month2 <=0) {
year2 = parseInt(year2) - parseInt(month2 / 12 == 0 ? 1 : parseInt(month2) / 12);
month2 = 12 - (Math.abs(month2) % 12);
}
var day2 = day;
var days2 = new Date(year2, month2, 0);
days2 = days2.getDate();
if (day2 > days2) {
day2 = days2;
}
if (month2 < 10) {
month2 = '0' + month2;
}
var t2 = year2 + '-' + month2 + '-' + day2;
return t2;
}