js获取当前日期的前几

1.获取当前的日期时间 格式“yyyy-MM-dd HH:MM:SS”

function getNowFormatDate() {
    var date = new Date();
    var seperator1 = "-";
    var seperator2 = ":";
    var month = date.getMonth() + 1;
    var strDate = date.getDate();
    if (month >= 1 && month <= 9) {
        month = "0" + month;
    }
    if (strDate >= 0 && strDate <= 9) {
        strDate = "0" + strDate;
    }
    var currentdate = date.getFullYear() + seperator1 + month + seperator1 + strDate
            + " " + date.getHours() + seperator2 + date.getMinutes()
            + seperator2 + date.getSeconds();
    return currentdate;
}

2.获取当前日期的前几个月

function beforeMonth(num){
  var date = new Date();      
  date.setMonth(date.getMonth()-num); 
  var year=date.getFullYear();  
  var month=date.getMonth()+1;
  month =(month<10 ? "0"+month:month);  
  sDate = (year.toString()+'-'+month.toString());
return sDate;
}

3.获取昨日及前几天

function getDay(num, str) {
        var today = new Date();
        var nowTime = today.getTime();
        var ms = 24*3600*1000*num;
        today.setTime(parseInt(nowTime + ms));
        var oYear = today.getFullYear();
        var oMoth = (today.getMonth() + 1).toString();
        if (oMoth.length <= 1) oMoth = '0' + oMoth;
        var oDay = today.getDate().toString();
        if (oDay.length <= 1) oDay = '0' + oDay;
        return oYear + str + oMoth + str + oDay;
    }
    
    var yesterday = getDay(-1, '-');        //    -1 代表前一天，-2前两天...
    console.log(yesterday);