第一种方法：
适合用在已经有取到没有格式化的数据了
//获取系统当前时间
var nowdate = new Date();
var y = nowdate.getFullYear();
var m = (nowdate.getMonth()+1).toString().padStart(2,'0');
var d = nowdate.getDate().toString().padStart(2,'0');
var currentTime = y+'-'+m+'-'+d;
that.date1=currentTime;
that.date3=currentTime;
//获取系统前一个月的时间
nowdate.setMonth(nowdate.getMonth()-1);
var y = nowdate.getFullYear();
var m = (nowdate.getMonth()+1).toString().padStart(2,'0');
var d = nowdate.getDate().toString().padStart(2,'0');
var preMonth = y+'-'+m+'-'+d;
that.date=preMonth;
that.date2=preMonth;
第二种方法
适用于时间戳转换日期的时候顺便补0
var change = new Date(that.dataList[i][0] * 1000);
var Y = change.getFullYear() + "-";
var M = (change.getMonth() + 1 < 10 ? "0" + (change.getMonth() + 1) : change.getMonth() + 1) + "-";
var D= (change.getDate() < 10 ? "0" + (change.getDate()) : change.getDate()) + " ";
var h= (change.getHours() < 10 ? "0" + (change.getHours()) : change.getHours()) + ":";
var m= (change.getMinutes() < 10 ? "0" + (change.getMinutes()) : change.getMinutes()) + ":";
var s= (change.getSeconds() < 10 ? "0" + (change.getSeconds()) : change.getSeconds());
var newDate = Y + M + D + h + m + s;
