<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>JavaScript
<body>
<table id="tb">
<tr>
<td>111111111111111</td>
</tr>
<tr>
<td>222222222222</td>
</tr>
<tr>
<td>33333333333</td>
</tr>
<tr>
<td>44444444444</td>
</tr>
<tr>
<td>55555555555</td>
</tr>
<tr>
<td>66666666</td>
</tr>
<tr>
<td>7777777777</td>
</tr>
<tr>
<td>8888888</td>
</tr>
<tr>
<td>9999999999</td>
</tr>
<tr>
<td>101010101010</td>
</tr>
</table>
</body>
<script type="text/javascript">
window.onload=function()
{
var tb =document.getElementById("tb");
var rows =tb.getElementsByTagName("tr");
for(i=0;i<rows.length;i++)
{
var j = parseInt(i/3);//用了自带函数parseInt解析成整数
alert(i/3);//不解析的值
if(j%2==0){
rows[i].style.backgroundColor="#f00";//背景红色
rows[i].style.color="#fff"; //字体白色
}else{
rows[i].style.backgroundColor="#0f0";//绿色
rows[i].style.color="#00f"; //蓝色
}
}
}
</script>
</html>