修改url中某个参数

function changeURLArg(url,arg,arg_val){
    var pattern=arg+'=([^&]*)';
    var replaceText=arg+'='+arg_val;
    if(url.match(pattern)){
        var tmp='/('+ arg+'=)([^&]*)/gi';
        tmp=url.replace(eval(tmp),replaceText);
        return tmp;
    }else{
        if(url.match('[\?]')){
            return url+'&'+replaceText;
        }else{
            return url+'?'+replaceText;
        }
    }
}