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>