鼠标悬浮tr追加背景颜色

.tr_on {
background: #3CF;
}

<table class="table" id="table">
<tr>
<td>11111111</td>
<td>111111111</td>
<td>11111111111</td>
<td>111111111111</td>
<td>1111111111111111</td>
</tr>
<tr>
<td>1</td>
<td>1</td>
<td>1</td>
<td>1</td>
<td>1</td>
</tr>
<tr>
<td>1</td>
<td>1</td>
<td>1</td>
<td>1</td>
<td>1</td>
</tr>
<tr>
<td>1</td>
<td>1</td>
<td>1</td>
<td>1</td>
<td>1</td>
</tr>
<tr>
<td>1</td>
<td>1</td>
<td>1</td>
<td>1</td>
<td>1</td>
</tr>
<tr>
<td>1</td>
<td>1</td>
<td>1</td>
<td>1</td>
<td>1</td>
</tr>
</table>

$('.table tr').hover(
function () {
$(this).addClass("tr_on");
},
function () {
$(this).removeClass("tr_on");
}
);