日期转换为yyyy-MM-dd HH:mm:ss格式

//获取当前时间日期
          function showTime() {
             var nowdate = new Date();
             console.log(nowdate);//Tue Mar 31 2020 16:09:28 GMT+0800 (中国标准时间)
             var nowtime =  new Date().getTime();
             console.log(nowtime);//1585642168717
             nowtime =  new Date(nowtime-24*60*60*1000);//昨天
             var date = nowtime.getDate();
             var y = nowtime.getFullYear();
             var m = nowtime.getMonth() + 1;
             var d = nowtime.getDate();
             var h = nowtime.getHours();
             var mm = nowtime.getMinutes();
             var s = nowtime.getSeconds();
             m = m < 10 ? '0' + m : m
             d = d < 10 ? '0' + d : d
             h = h < 10 ? '0' + h : h
             mm = mm < 10 ? '0' + mm : mm
             s = s < 10 ? '0' + s : s
             var mytime =  y + '-' + m + '-' + d + ' ' + h + ':' + mm + ':' + s;
             console.log(mytime);
          }
          showTime();