Date.prototype.Format = 
function (fmt) { 
    var o = {  
        
"M+": 
this.getMonth() + 
1, 
        
"d+": 
this.getDate(), 
        
"H+": 
this.getHours(), 
        
"m+": 
this.getMinutes(), 
        
"s+": 
this.getSeconds(), 
        
"q+": 
Math.floor((
this.getMonth() + 
3) / 
3), 
        
"S": 
this.getMilliseconds() 
    };  
    
if (
/(y+)/.test(fmt)) fmt = fmt.replace(
RegExp.$
1, (
this.getFullYear() + 
"").substr(
4 - 
RegExp.$
1.length));  
    
for (
var k 
in o)  
    
if (
new RegExp(
"(" + k + 
")").test(fmt)) fmt = fmt.replace(
RegExp.$
1, (
RegExp.$
1.length == 
1) ? (o[k]) : ((
"00" + o[k]).substr((
"" + o[k]).length)));  
    
return fmt;  
}  
调用:   
var time1 = 
new Date().Format(
"yyyy-MM-dd");  
var time2 = 
new Date().Format(
"yyyy-MM-dd HH:mm:ss");  
var nowTime=
new Date();  
nowTime.setMonth(nowTime.getMonth()-
1);    
alert(nowTime.Format(
"yyyy-MM-dd HH:mm:ss");)