Js empty data table in the tbody

1, HTML structure

<table id = "test">
    <thead>
        <tr><td>列1</td><td>列2</td><td>列3</td><td>列4</td></tr>
    </thead>
    <tbody>
        <tr><td>1</td><td>1</td><td>2</td><td>3</td></tr>
        <tr><td>2</td><td>4</td><td>5</td><td>6</td></tr>
        <tr><td>3</td><td>7</td><td>8</td><td>9</td></tr>
        <tr><td>4</td><td>1</td><td>2</td><td>3</td></tr>
    </tbody>     
</table>
<input type="button" id="btn"value = "Clear" >

2, jquery Code

$(function(){
    $("#btn").click(function() {
        $("#test tbody").html("");
    });
});