js 将时间戳转为日期格式

最近项目需要在前端将一个13位的时间戳显示成日期格式，在网上查了很多都不符合要求，只有一个是能满足要求的，在这记录一下，说不定以后还用的着。

13位时间戳改为yyyy-MM-dd HH-mm-ss 格式 
目标时间戳：1516324500000

  //将时间戳改为yyyy-MM-dd HH-mm-ss
    function formatDateTime(unix) {
        var now = new Date(parseInt(unix) * 1);
        now =  now.toLocaleString().replace(/年|月/g, "-").replace(/日/g, " ");
        if(now.indexOf("下午") > 0) {
            if (now.length == 18) {
                var temp1 = now.substring(0, now.indexOf("下午"));   //2014/7/6
                var temp2 = now.substring(now.indexOf("下午") + 2, now.length);  // 5:17:43
                var temp3 = temp2.substring(0, 1);    //  5
                var temp4 = parseInt(temp3); // 5
                temp4 = 12 + temp4;  // 17
                var temp5 = temp4 + temp2.substring(1, temp2.length); // 17:17:43
                now = temp1 + temp5; // 2014/7/6 17:17:43
                now = now.replace("/", "-"); //  2014-7/6 17:17:43
                now = now.replace("/", "-"); //  2014-7-6 17:17:43
            }else {
                var temp1 = now.substring(0, now.indexOf("下午"));   //2014/7/6
                var temp2 = now.substring(now.indexOf("下午") + 2, now.length);  // 5:17:43
                var temp3 = temp2.substring(0, 2);    //  5
                if (temp3 == 12){
                    temp3 -= 12;
                }
                var temp4 = parseInt(temp3); // 5
                temp4 = 12 + temp4;  // 17
                var temp5 = temp4 + temp2.substring(2, temp2.length); // 17:17:43
                now = temp1 + temp5; // 2014/7/6 17:17:43
                now = now.replace("/", "-"); //  2014-7/6 17:17:43
                now = now.replace("/", "-"); //  2014-7-6 17:17:43
            }
        }else {
            var temp1 = now.substring(0,now.indexOf("上午"));   //2014/7/6
            var temp2 = now.substring(now.indexOf("上午")+2,now.length);  // 5:17:43
            var temp3 = temp2.substring(0,1);    //  5
            var index = 1;
            var temp4 = parseInt(temp3); // 5
            if(temp4 == 0 ) {   //  00
                temp4 = "0"+temp4;
            }else if(temp4 == 1) {  // 10  11  12
                index = 2;
                var tempIndex = temp2.substring(1,2);
                if(tempIndex != ":") {
                    temp4 = temp4 + "" + tempIndex;
                }else { // 01
                    temp4 = "0"+temp4;
                }
            }else {  // 02 03 ... 09
                temp4 = "0"+temp4;
            }
            var temp5 = temp4 + temp2.substring(index,temp2.length); // 07:17:43
            now = temp1 + temp5; // 2014/7/6 07:17:43
            now = now.replace("/","-"); //  2014-7/6 07:17:43
            now = now.replace("/","-"); //  2014-7-6 07:17:43
        }
        return now;
    };
    alert(formatDateTime(1516324500000));