JS将时间戳转换为日期时间格式

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));

结果如下：