Get a specific value in the url query string

<script>
        function getUrlParam(name) {
    
    
            var reg = new RegExp("(^|&)" + name + "=([^&]*)(&|$)"); //构造一个含有目标参数的正则表达式对象
            var r = window.location.search.substr(1).match(reg);  //匹配目标参数
            if (r != null) return decodeURI(r[2]);
            return null; //返回参数值
        }
        
    </script>