<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>菜鸟教程(runoob.com)</title>
<script>
function displayResult(){
    alert(document.getElementById('myTable').tFoot.innerHTML);
}
</script>
</head>
<body>

<table id="myTable" border="1">
    <thead>
        <tr>
            <th>Month</th>
            <th>Savings</th>
    </tr>
    </thead>
    <tfoot>
        <tr>
            <td>Sum</td>
            <td>$180</td>
    </tr>
</tfoot>
<tbody>
     <tr>
         <td>January</td>
         <td>$100</td>
     </tr>
     <tr>
         <td>February</td>
         <td>$80</td>
     </tr>
</tbody>
</table>
<br>
<button type="button" onclick="displayResult()">显示底部内容</button>

</body>
</html>