HTMLSelectElement

这个接口从 HTMLElement，Element 和 Node 继承属性。

HTMLSelectElement.autofocus (en-US)

A Boolean reflecting the autofocus HTML attribute, which indicates whether the control should have input focus when the page loads, unless the user overrides it, for example by typing in a different control. Only one form-associated element in a document can have this attribute specified.

HTMLSelectElement.disabled (en-US)

A Boolean reflecting the disabled HTML attribute, which indicates whether the control is disabled. If it is disabled, it does not accept clicks.

HTMLSelectElement.form (en-US)只读

An HTMLFormElement referencing the form that this element is associated with. If the element is not associated with of a <form> element, then it returns null.

HTMLSelectElement.labels (en-US)只读

A NodeList of <label> elements associated with the element.

HTMLSelectElement.length

An unsigned long The number of <option> elements in this select element.

HTMLSelectElement.multiple

A Boolean reflecting the multiple HTML attribute, which indicates whether multiple items can be selected.

HTMLSelectElement.name

A DOMString reflecting the name HTML attribute, containing the name of this control used by servers and DOM search functions.

HTMLSelectElement.options (en-US)只读

An HTMLOptionsCollection (en-US) representing the set of <option> (HTMLOptionElement) elements contained by this element.

HTMLSelectElement.required

A Boolean reflecting the required HTML attribute, which indicates whether the user is required to select a value before submitting the form.

HTMLSelectElement.selectedIndex

A long reflecting the index of the first selected <option> element. The value -1 indicates no element is selected.

HTMLSelectElement.selectedOptions (en-US)只读

An HTMLCollection representing the set of <option> elements that are selected.

HTMLSelectElement.size

A long reflecting the size HTML attribute, which contains the number of visible items in the control. The default is 1, unless multiple is true, in which case it is 4.

HTMLSelectElement.type (en-US)只读

A DOMString represeting the form control's type. When multiple is true, it returns "select-multiple"; otherwise, it returns "select-one".

HTMLSelectElement.validationMessage只读

A DOMString representing a localized message that describes the validation constraints that the control does not satisfy (if any). This attribute is the empty string if the control is not a candidate for constraint validation (willValidate is false), or it satisfies its constraints.

HTMLSelectElement.validity只读

A ValidityState reflecting the validity state that this control is in.

HTMLSelectElement.value

A DOMString reflecting the value of the form control. Returns the value property of the first selected option element if there is one, otherwise the empty string.

HTMLSelectElement.willValidate只读

A Boolean that indicates whether the button is a candidate for constraint validation. It is false if any conditions bar it from constraint validation.

这个接口从 HTMLElement，Element 和 Node 继承属性。

HTMLSelectElement.add()

Adds an element to the collection of option elements for this select element.

HTMLSelectElement.blur() 已弃用

Removes input focus from this element. This method is now implemented on HTMLElement.

HTMLSelectElement.checkValidity()

Checks whether the element has any constraints and whether it satisfies them. If the element fails its constraints, the browser fires a cancelable invalid event at the element (and returns false).

HTMLSelectElement.focus() 已弃用

Gives input focus to this element. This method is now implemented on HTMLElement.

HTMLSelectElement.item() (en-US)

Gets an item from the options collection for this <select> element. You can also access an item by specifying the index in array-style brackets or parentheses, without calling this method explicitly.

HTMLSelectElement.namedItem() (en-US)

Gets the item in the options collection with the specified name. The name string can match either the id or the name attribute of an option node. You can also access an item by specifying the name in array-style brackets or parentheses, without calling this method explicitly.

HTMLSelectElement.remove()

Removes the element at the specified index from the options collection for this select element.

HTMLSelectElement.reportValidity()

This method reports the problems with the constraints on the element, if any, to the user. If there are problems, it fires a cancelable invalid event at the element, and returns false; if there are no problems, it returns true.

HTMLSelectElement.setCustomValidity()

Sets the custom validity message for the selection element to the specified message. Use the empty string to indicate that the element does not have a custom validity error.

使用 addEventListener() 或给下面接口的 oneventname 属性分配一个监听程序来监听这些事件：

input 事件

当 <input>, <select>, 或 <textarea> 元素的 value 改变时触发该事件。

/* assuming we have the following HTML
<select id='s'>
    <option>First</option>
    <option selected>Second</option>
    <option>Third</option>
</select>
*/

var select = document.getElementById('s');

// return the index of the selected option
console.log(select.selectedIndex); // 1

// return the value of the selected option
console.log(select.options[select.selectedIndex].value) // Second

A better way to track changes to the user's selection is to watch for the change event to occur on the <select>. This will tell you when the value changes, and you can then update anything you need to. See the example provided in the documentation for the change event for details.

• <select> HTML 元素