javascript - 我可以将所需属性应用于HTML5中的<select>字段吗？(Can I apply the required attribute to <select> fields in HTML5?)

Question

How can I check if a user has selected something from a <select> field in HTML5?

(如何检查用户是否从HTML5中的<select>字段中选择了某些内容？)

I see <select> doesn't support the new required attribute... do I have to use JavaScript then?

(我看到<select>不支持新的required属性...那么我必须使用JavaScript吗？)

Or is there something I'm missing?

(还是有什么我想念的？)

:/

(：/)

  ask by Matt translate from so

Answer 1

Mandatory : Have the first value empty - required works on empty values

(必填 ：将第一个值设为空 - 必需对空值起作用)

Prerequisites : correct html5 DOCTYPE and a named input field

(先决条件 ：正确的html5 DOCTYPE和命名输入字段)

<select name="somename" required>
<option value="">Please select</option>
<option value="one">One</option>
</select>

As per the documentation (the listing and bold is mine)

(根据文档 （列表和粗体是我的）)

The required attribute is a boolean attribute.

(required属性是布尔属性。)

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

(指定后，用户需要在提交表单之前选择一个值。)

If a select element

(如果是一个选择元素)

• has a required attribute specified,

  (指定了必需属性，)

• does not have a multiple attribute specified,

  (没有指定多个属性，)

• and has a display size of 1 (do not have SIZE=2 or more - omit it if not needed);

  (并且显示尺寸为1（没有SIZE = 2或更多 - 如果不需要则省略它）;)

• and if the value of the first option element in the select element's list of options (if any) is the empty string (ie present as value="" ),

  (如果select元素的选项列表中的第一个选项元素的值（如果有的话）是空字符串 （即表示为value="" ），)

• and that option element's parent node is the select element (and not an optgroup element),

  (并且该选项元素的父节点是select元素（而不是optgroup元素），)

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

(然后该选项是select元素的占位符标签选项。)