javascript - 如何使用 jQuery 制作一个必需的选择框？

Question

记住这一点

$("div input[id = 'weight']").attr('required','required');

如何将它用于选择框#cargo以使其成为必需？

Answer 1

是的，可以将 required 属性添加到 select 元素，只要第一个 option 的值为 ""，一个空字符串。

注意: 必需 不支持< IE9

示例:

$('select#required').attr('required',1);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<form>

  <select id="required">
    <option value="">Please select</option>
    <option value="one">One</option>
    <option value="two">Two</option>
    <option value="three">Three</option>
  </select>

  <input type="submit" value="Submit" />

</form>

文档:(粗体文本很重要，但不在文档中)

http://dev.w3.org/html5/spec-author-view/the-select-element.html#the-select-element

The required attribute is a boolean attribute.
When specified, the user will be required to select a value before submitting the form.

If a select element

• has a required attribute specified,
• does not have a multiple attribute specified,
• and has a display size of 1;
• and if the value of the first option element in the select element's list of options (if any) is the empty string,
• and that option element's parent node is the select element (and not an optgroup element),

then that option is the select element's placeholder label option.