我有一个如下的表单:
var x = document.getElementById("submit-button");
if (x.selectedIndex.value == null) {
$("#submit-button").css("display","none");
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form>
<select>
<option disabled selected>Select colour</option>
<option value="Orange">Orange</option>
<option value="Apple">Apple</option>
<option value="Lemon">Lemon</option>
</select>
<button id="submit-button" type="submit">Click</button>
</form>
任何帮助都将不胜感激。