异步处理未登录url跳转

// 从url中获取原页面url=http://localhost:8080/xxx/oldurl
function GetQueryString(paras){ 
    var url = location.href;  
    var paraString = url.substring(url.indexOf("?")+1,url.length).split("&");  
    var paraObj = {}  
    for (i=0; j=paraString[i]; i++){  
        paraObj[j.substring(0,j.indexOf("=")).toLowerCase()] = j.substring(j.indexOf("=")+1,j.length);  
    }  
    var returnValue = paraObj[paras.toLowerCase()];  
    if(typeof(returnValue)=="undefined"){  
        return "";  
    }else{  
        return returnValue; 
    }
}
// 异步登录成功后跳转回原来页面http://localhost:8080/xxx/oldurl
var url = GetQueryString("url"); 
if(url!=null&&url!=undefined&&url!=‘‘){
    window.location.href=url; 
    return;
}