JavaScript如何实现将时间戳转换成日期格式

/**
 * [TimeToDate时间戳转换为日期]
 * @param {[type]} unixTime [时间戳]
 * @param {String} type     [Y-m-d,Y-m-d H:i:s,Y/m/d,Y/m/d H:i:s,Y年m月d日,Y年m月d日 H:i:s]
 */
function TimeToDate(unixTime,type="Y-M-D H:i:s"){
    var date = new Date(unixTime * 1000);//时间戳为10位需*1000，时间戳为13位的话不需乘1000
    var datetime = "";
    datetime += date.getFullYear() + type.substring(1,2);
    datetime += (date.getMonth()+1 < 10 &#63; '0'+(date.getMonth()+1) : date.getMonth()+1) + type.substring(3,4);
    datetime += (date.getDate() < 10 &#63; '0'+(date.getDate()) : date.getDate());
    if (type.substring(5,6)) {
        if (type.substring(5,6).charCodeAt() > 255) {
            datetime += type.substring(5,6);
            if (type.substring(7,8)) {
                datetime += " " + (date.getHours() < 10 &#63; '0'+(date.getHours()) : date.getHours());
                if (type.substring(9,10)) {
                    datetime += type.substring(8,9) + (date.getMinutes() < 10 &#63; '0'+(date.getMinutes()) : date.getMinutes());
                    if (type.substring(11,12)) {
                        datetime += type.substring(10,11) + (date.getSeconds() < 10 &#63; '0'+(date.getSeconds()) : date.getSeconds());
                    };
                };
            };
        }else{
            datetime += " " + (date.getHours() < 10 &#63; '0'+(date.getHours()) : date.getHours());
            if (type.substring(8,9)) {
                datetime += type.substring(7,8) + (date.getMinutes() < 10 &#63; '0'+(date.getMinutes()) : date.getMinutes());
                if (type.substring(10,11)) {
                    datetime += type.substring(9,10) + (date.getSeconds() < 10 &#63; '0'+(date.getSeconds()) : date.getSeconds());
                };
            };
        };
    };
    return datetime;
}

TimeToDate("1515640111");    //2018-01-11 11:08:31
TimeToDate("1515640111","Y-m-d");    //2018-01-11
TimeToDate("1515640111","Y-m-d H:i");    //2018-01-11 11:08
TimeToDate("1515640111","Y-m-d H:i:s");    //2018-01-11 11:08:31
TimeToDate("1515640111","Y/m/d");    //2018/01/11
TimeToDate("1515640111","Y/m/d H:i:s");    //2018/01/11 11:08:31
TimeToDate("1515640111","Y年m月d日");    //2018年01月11日
TimeToDate("1515640111","Y年m月d日 H:i:s");    //2018年01月11日 11:08:31

/**
 * [DateToTime 日期转换时间戳]
 * @param {[type]} day [日期格式，仅支持标准格式]
 */
function DateToTime(day){
	// re = /(\d{4})(?:-(\d{1,2})(?:-(\d{1,2}))?)?(?:\s+(\d{1,2}):(\d{1,2}):(\d{1,2}))?/.exec(day); // 原
	re = /(\d{4})(?:\D?(\d{1,2})(?:\D?(\d{1,2}))?[^\d\s]?)?(?:\s+(\d{1,2})\D?(\d{1,2})\D?(\d{1,2}))?/.exec(day);
	return new Date(re[1],(re[2]||1)-1,re[3]||1,re[4]||0,re[5]||0,re[6]||0).getTime()/1000;
}
DateToTime("2018-01-11 11:08:31");
DateToTime("2018-01-11");
DateToTime("2018年01月11日 11时08分31秒");
DateToTime("2018");

function TimeToDate(date,format) {
  format = format || 'YYYY-MM-DD hh:mm:ss';
  var dateTest = (/^(-)?\d{1,10}$/.test(date) || /^(-)?\d{1,13}$/.test(date));
  if(/^[1-9]*[1-9][0-9]*$/.test(date) && dateTest){
    var vdate = parseInt(date);
    if (/^(-)?\d{1,10}$/.test(vdate)) {
      vdate = vdate * 1000;
    } else if (/^(-)?\d{1,13}$/.test(vdate)) {
      vdate = vdate * 1000;
    } else if (/^(-)?\d{1,14}$/.test(vdate)) {
      vdate = vdate * 100;
    } else {
      alert("时间戳格式不正确");
      return;
    }
    var setdate = new Date(vdate);
    return parse({YYYY:setdate.getFullYear(), MM:digit(setdate.getMonth()+1), DD:digit(setdate.getDate()) , hh:digit(setdate.getHours()), mm:digit(setdate.getMinutes()), ss:digit(setdate.getSeconds()) }, format);
  }else {
    //将日期转换成时间戳
    var arrs = date.match(/\w+|d+/g),
      newdate = new Date(arrs[0],parseInt(arrs[1])-1,arrs[2],arrs[3]||0,arrs[4]||0,arrs[5]||0),
      timeStr = Math.round(newdate.getTime() / 1000);
    return timeStr;
  }

  function parse(ymdhms, format) {
    var regymdzz = "YYYY|MM|DD|hh|mm|ss|zz";
    return format.replace(new RegExp(regymdzz,"g"), function(str, index) {
      return str == "zz" ? "00":digit(ymdhms[str]);
    });
  };
  function digit(num) {
    return num < 10 &#63; "0" + (num | 0) :num;
  };
};