从下拉菜单中未选择任何选项时禁用按钮

Question

我有一个输入类型按钮（由于它触发了表单内的辅助动作，因此无法提交类型），如果在上一个下拉选择器上未进行选择，则需要保持禁用状态。我尝试失败了：this，this，this和其他一些...

这是我的表单代码：

echo "<select class='corpusname' id='corpusname' size='1' name='corpusname' required />
<option value=''>Select a corpus</option>";

// This query gives the other options from a database
$result = mysqli_query($db, "SELECT * FROM corpus_info") or die(mysqli_error($db));
while($cpsmlg = mysqli_fetch_array($result)){
echo "<option value='".$cpsmlg['corpus']."'>".$cpsmlg['title']."</option>";
}
echo "</select>
<a id='theLink' target='_blank'>

// This is the button to be disabled
<input type='button' id='seedoc' class='seedoc' value='See doc' /></a>";

Answer 1

只需向中添加一个onchange事件select。

function enableButton()
{
    var selectelem = document.getElementById('corpusname');
    var btnelem = document.getElementById('seedoc');
    btnelem.disabled = !selectelem.value;
}

<select class='corpusname' id='corpusname' size='1' name='corpusname' required onchange="enableButton()"/>
<option value=''>Select a corpus</option>
<option value="1">1</option>
</select>
<input type="button" id="seedoc" disabled value="Submit">