JavaScript获取距离某天前或后的日期详解编程语言

/**  
* param  Date Object：Mon May 11 13:53:08 UTC+0800 2015   
* n 自param 起向后多少天  
* return Date Object：Mon May 11 13:53:08 UTC+0800 2015  
*/  
function getDateBeforeParamDate(param,n){  
var result = new Date();  
if(param==null){  
param = result;  
}  
if(n==null){  
n=0;  
}  
param = new Date(param);  
millSecond = param.valueOf();  
millSecond =  millSecond - n*24*3600*1000;  
result = new Date(millSecond);  
result = getTodayFormatea(result);  
return result;  
}  
/**  
* param  Date对象：Mon May 11 13:53:08 UTC+0800 2015   
* n 自param 向前多少天  
* return Date Object：Mon May 11 13:53:08 UTC+0800 2015  
*/  
function getDateNextParamDate(param,n){  
var result = new Date();  
if(param==null){  
param = result;  
}  
if(n==null){  
n=0;  
}  
param = new Date(param);  
millSecond = param.valueOf();  
millSecond = millSecond + n*24*3600*1000;  
result = new Date(millSecond);  
result = getTodayFormatea(result);  
return result;  
}