JS获取url参数：如果不存在参数，自动跳转到指定页面

<div id="bgtm">
  <a href='1.html?id=12&grade=0'>成绩</a>
</div>
<script>
  function GetUrlParam(paraName) {
    var url = document.location.toString();
    var arrObj = url.split("?");
    if (arrObj.length > 1) {
      var arrPara = arrObj[1].split("&");
      var arr;
      for (var i = 0; i < arrPara.length; i++) {
        arr = arrPara[i].split("=");
        if (arr != null && arr[0] == paraName) {
          return arr[1];
        }
      }
      return "";
    }
    else {
      alert('参数错误!');
      window.location.href="1.html?id=12&grade=0";
    }
  }
  console.log(GetUrlParam("grade"));
</script>