js毫秒级时间戳转为日期

function format(time, format) {
        var t = new Date(time);
        var tf = function(i) {
          return (i < 10 ? "0" : "") + i;
        };
        return format.replace(/yyyy|MM|dd|HH|mm|ss/g, function(a) {
          switch (a) {
            case "yyyy":
              return tf(t.getFullYear());
              break;
            case "MM":
              return tf(t.getMonth() + 1);
              break;
            case "mm":
              return tf(t.getMinutes());
              break;
            case "dd":
              return tf(t.getDate());
              break;
            case "HH":
              return tf(t.getHours());
              break;
            case "ss":
              return tf(t.getSeconds());
              break;
          }
        });
      }

//调用
 format('1596598909823',yyyy-MM-dd HH:mm:ss'),