Javascript获取url中的参数值

javascript的实现代码如下:

    function QueryString(fieldName)
    { 
var urlString = document.location.search;
if(urlString != null)
      {
var typeQu = fieldName+"=";
var urlEnd = urlString.indexOf(typeQu);
if(urlEnd != -1)
           {
var paramsUrl = urlString.substring(urlEnd+typeQu.length);
var isEnd =  paramsUrl.indexOf('&');
if(isEnd != -1)
                {
return paramsUrl.substring(0, isEnd);
                }
else
                {
return paramsUrl;
                }
           }
else
           {
return null;
           }
      }
else
     {
return null;
     }
    }