根据已知日期（yyyy-MM-dd）获取前n天的日期区间

//获取天
var  pubTime="2017-12-30"
 function buildDay(num){
                num=num-1;
                var myDate = new Date(pubTime); //获取今天日期
                myDate.setDate(myDate.getDate() - num);
                var dateArray = [];
                var dateTemp;
                var flag = 1;
                for (var i = 0; i < num; i++) {
                    var month=myDate.getMonth()+1
                    if(month<10){
                        month="0"+month;
                    }
                    var day=myDate.getDate()
                    if(day<10){
                        day="0"+day;
                    }
                    dateTemp =myDate.getFullYear()+""+ month+""+day;
                    dateArray.push(dateTemp);
                    myDate.setDate(myDate.getDate() + flag);
                }
                dateArray.push(pubTime.replace(/-/g,""))
                return dateArray
            }

//获取月分

function buildMonth(months){

    var now = new Date(pubTime);
    var cur_month = now.getMonth();
    now.setDate(1);//重置成1号，原因：在做减月份时，减去的月份没有31号，会自动加1到下个月份，导致计算失误

    if(months < 0){
        var _m = cur_month+months + 1;
        now.setMonth(_m);
    }

    var _months = [];
    for(var i = 0 ; i < Math.abs(months) ; i++){
        var year = now.getFullYear();
        var month = now.getMonth();
        if(i != 0 ){
            now.setMonth(month+1);
        }
        year = now.getFullYear();
        var _month = now.getMonth()+1;
        if(_month < 10) _month = '0'+_month;
        else _month = _month.toString();
        _months.push(year+_month);
    }
    //console.log('buildMonthData============>'+_months);
    return _months;
},