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請教第九章編程挑戰(zhàn)~無法刪除、添加，顏色不改變~求高手指點，謝謝

<!DOCTYPE?html>
<html>
?<head>
??<title>?new?document?</title>??
??<meta?http-equiv="Content-Type"?content="text/html;?charset=gbk"/>???
??<script?type="text/javascript">?
??
??????window.onload?=?function(){
??????????????????
?????//?鼠標(biāo)移動改變背景,可以通過給每行綁定鼠標(biāo)移上事件和鼠標(biāo)移除事件來改變所在行背景色。
?????????var?hang=document.getElementsByTagName("tr");
?????????for(var?i=0;i<hang.length;i++)
?????????{
?????????????color(hang[i]);
?????????}
	?}
	?
?????function?color(obj)
????{
????????obj.onmouseover=function(){obj.style.backgroundColor="#f2f2f2";
????????obj.onmouseout=function(){obj.style.backgroundColor="#fff";
????}
??????//?編寫一個函數(shù)，供添加按鈕調(diào)用，動態(tài)在表格的最后一行添加子節(jié)點；
?????var??num=2;
?????function?makeup()
?????{
?????????num++;
?????????var?newname=document.createElement("tr");
?????????var?new1=document.createElement("td");
?????????var?new2=document.createElement("td");
?????????var?table=document.getElementById("table");
?????????new1.innerHTML="xh0"+num;
?????????new2.innerHTML="第"+num+"學(xué)生";
?????????var?new3=document.createElement("td");
?????????new3.innerHTML="<a?href="javascript:;"?onclick='mydelete(this)'>刪除</a>";
?????????table.appendChild(newname);
?????????newname.appendChild(new1);
?????????newname.appendChild(new2);
?????????newname.appendChild(new3);
?????????
?????????var?hang=document.getElementsByTagName("tr");
?????????for(var?i=0;i<hang.length;i++)
?????????{
?????????????color(hang[i]);
?????????}
?????}
????		
???	?
?????//?創(chuàng)建刪除函數(shù)
?????function?mydelete(obj)
?????{
?????????var?table=obj.parentNode.parentNode.parentNode;
?????????var?mytr=obj.parentNode.parentNode;
?????????table.removeChild(mytr);
?????}

??</script>?
?</head>?
?<body>?
	???<table?border="1"?width="50%"?id="table">
	???<tr>
		<th>學(xué)號</th>
		<th>姓名</th>
		<th>操作</th>
	???</tr>??

	???<tr>
		<td>xh001</td>
		<td>王小明</td>
		<td><a?href="javascript:;"?onclick="mydelete(this)">刪除</a></td>???<!--在刪除按鈕上添加點擊事件??-->
	???</tr>

	???<tr>
		<td>xh002</td>
		<td>劉小芳</td>
		<td><a?href="javascript:;"?onclick="mydelete(this)">刪除</a></td>???<!--在刪除按鈕上添加點擊事件??-->
	???</tr>??

	???</table>
	???<input?type="button"?value="添加一行"?onclick="makeup()"?/>???<!--在添加按鈕上添加點擊事件??-->
?</body>
</html>