JavaScript实现时间戳转换为“xx天前”显示格式

<!DOCTYPE html>
<html>
<head>
< http-equiv="Content-Type" content="text/html; charset=utf-8"/>
< src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js">
</ > 
< > $(document).ready(function()
{ 
var str = ""; 
var timestamp = 0; 
var pass = 0;  
str = $("#time").text(); 
timestamp = (new Date()).valueOf(); 
pass = (timestamp - str) / 1000;  
$("#time").text(pass); 
if (pass < 60) {  
$("#time").text(pass + "秒前"); 
} 
else
{  
if (pass < (60 * 60)) 
{  
pass = Math.floor(pass / 60);  
$("#time").text(pass + "分钟前");  
}
else 
{  
if (pass < (60 * 60 * 72))
{   
pass = Math.floor(pass / 60 / 60);   
$("#time").text(pass + "小时前");   
} 
else
{   
if (pass >= (60 * 60 * 72) )
{    
pass = Math.floor(pass / 60 / 60 / 24);   
$("#time").text(pass + "天前");   
}  
}  
} 
} 
});
</ > 
</head> 
<body> 
<div id="time">1486122654000</div>
</body> 
</html>