给页面路径加上或修改某参数(js操作)

<script type="text/javascript">                //每页显示指定个数商品        function getListPerPagesize(size)        {            location.href = urlAddOrUpdatePara(document.location.href, "pagesize", size);        }        //给页面路径加上或修改某参数        function urlAddOrUpdatePara(url, para, val)        {            var _index = url.lastIndexOf("?");            if (_index > 0)            {                if (_index < (url.length - 1))//?号不是最后字符                {                    var _value = getparmByUrl(para);                    if (_value != "")//路径已经有该参数                        url = setParaValue(url, para, val);//修改参数                    else                        url += "&" + para + "=" + val;                }                else                    url += para + "=" + val;            }            else                url += "?" + para + "=" + val;                        return url;             }                //获取url参数        function getparmByUrl(parmName) {            var url = window.location.toString();            var arr = url.split("?");            var parms = arr[1];            var parmList = parms.split("&");            var parmTemp;            for (var i = 0; i < parmList.length; i++) {                parmTemp = parmList[i].split("=");                if (parmTemp[0] == parmName)//存在该参数                    return parmTemp[1];            }            return ""        }                //修改url中某参数的值        function setParaValue(url, parama, val)        {            var strOne, strTwo, result;            var index = url.lastIndexOf(parama);            strOne = url.substr(0, index);//获取参数前面部分            strTwo = url.substr((index + 1));            var twoIndex = strTwo.lastIndexOf("&");//判断参数后面是否还有其他参数            if (twoIndex > 0)                strTwo = strTwo.substr(twoIndex);//获取后面参数包含"&"            else                strTwo = "";                        result = strOne + parama + "=" + val + strTwo;            return result;        }                 </script>