js table crossed and discolored
<head>
<title>Task</title>
<style type="text/css">
table {
margin: 0 auto;
border: 1px solid blue;
width: 400px;
height: 300px;
}
td {
border: 1px solid blue;
width: 30px;
}
</style>
<script type="text/javascript">
window.onload=function(){
var a=document.getElementsByTagName('tr'); for(var i=1;i<a.length;i++){ var mytr=a[i]; var oldcolor; mytr.onmouseover=function(){ oldcolor=this.style.background; this.style.background='#f1f1f1'; } mytr.onmouseout=function(){
this.style.background=oldcolor; } } } function cb(x){ var zt= x.checked; var f=document.getElementsByName('chek'); for(i=0;i<f.length;i++){ var xz=f[i]; xz.checked=zt; } } </script> </head> <body> <table> <tr> <td><input type="checkbox" onclick="cb(this)" /> 全选</td> <td>姓名</td> <td>性别</td> <td>年龄</td> <td>操作</td> </tr> <tr> <td><input type="checkbox" name="chek" /></td> <td>李一</td> <td>男</td>
<td>20</td>
<td><a href="">del</a></td>
</tr>
<tr>
<td><input type="checkbox" name="chek" /></td>
<td>李一</td>
<td>男</td>
<td>20</td>
<td><a href="">del</a></td>
</tr>
<tr>
<td><input type="checkbox" name="chek" /></td>
<td>李一</td>
<td>男</td>
<td>20</td>
<td><a href="">del</a></td>
</tr>
<tr>
<td><input type="checkbox" name="chek" /></td>
<td>李一</td>
<td>男</td>
<td>20</td>
<td><a href="">del</a></td>
</tr>
</table>
</body>
</html>