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Checkbox

A checkbox on an HTML form. A checkbox is a toggle switch that lets the user set a value on or off.

客户端对象
实现版本 Navigator 2.0
Navigator 3.0: 添加了 type 属性; 添加了 onBlur and onFocus event handlers; 添加了 blur and focus 方法s.
Navigator 4.0: 添加了 handleEvent 方法。

创建源

The HTML INPUT tag, with "checkbox" as the value of the TYPE attribute. For a given form, the JavaScript runtime engine creates appropriate Checkbox objects and puts these objects in the elements array of the corresponding Form object. You access a Checkbox object by indexing this array. You can index the array either by number or, if supplied, by using the value of the NAME attribute.

事件句柄

onBlur

onClick

onFocus

描述

A Checkbox object on a form looks as follows:

A Checkbox object is a form element and must be defined within a FORM tag.

Use the checked property to specify whether the checkbox is currently checked. Use the defaultChecked property to specify whether the checkbox is checked when the form is loaded or reset.

属性概览

checked Boolean 属性 that reflects the current state of the checkbox.
defaultChecked Boolean 属性 that reflects the CHECKED attribute.
form Specifies the form containing the Checkbox object.
name Reflects the NAME attribute.
type Reflects the TYPE attribute.
value Reflects the TYPE attribute.

方法概览

blur Removes focus from the checkbox.
click Simulates a mouse-click on the checkbox.
focus Gives focus to the checkbox.
handleEvent 调用指定事件的控制句柄。

示例

示例 1. The following example displays a group of four checkboxes that all appear checked by default:

<B>Specify your music preferences (check all that apply):</B>
<BR><INPUT TYPE="checkbox" NAME="musicpref_rnb" CHECKED> R&B
<BR><INPUT TYPE="checkbox" NAME="musicpref_jazz" CHECKED> Jazz
<BR><INPUT TYPE="checkbox" NAME="musicpref_blues" CHECKED> Blues
<BR><INPUT TYPE="checkbox" NAME="musicpref_newage" CHECKED> New Age 示例 2. The following example contains a form with three text boxes and one checkbox. The user can use the checkbox to choose whether the text fields are converted to uppercase. Each text field has an onChange event handler that converts the field value to uppercase if the checkbox is checked. The checkbox has an onClick event handler that converts all fields to uppercase when the user checks the checkbox.

<HTML>
<HEAD>
<TITLE>Checkbox object example</TITLE>
</HEAD>
<SCRIPT>
function convertField(field) {
   if (document.form1.convertUpper.checked) {
      field.value = field.value.toUpperCase()}
}
function convertAllFields() {
   document.form1.lastName.value = document.form1.lastName.value.toUpperCase()
   document.form1.firstName.value = document.form1.firstName.value.toUpperCase()
   document.form1.cityName.value = document.form1.cityName.value.toUpperCase()
}
</SCRIPT>
<BODY>
<FORM NAME="form1">
<B>Last name:</B>
<INPUT TYPE="text" NAME="lastName" SIZE=20 onChange="convertField(this)">
<BR><B>First name:</B>
<INPUT TYPE="text" NAME="firstName" SIZE=20 onChange="convertField(this)">
<BR><B>City:</B>
<INPUT TYPE="text" NAME="cityName" SIZE=20 onChange="convertField(this)">
<P><INPUT TYPE="checkBox" NAME="convertUpper"
   onClick="if (this.checked) {convertAllFields()}"
   > Convert fields to upper case
</FORM>
</BODY>
</HTML>

参看

Form, Radio

属性

checked

A Boolean value specifying the selection state of the checkbox.

属性源 Checkbox
实现版本 Navigator 2.0

安全性

Navigator 3.0：该属性默认是带有污点的。有关数据污点的更多信息，请看“JavaScript 的安全性”。

描述

If a checkbox button is selected, the value of its checked property is true; otherwise, it is false.

You can set the checked property at any time. The display of the checkbox button updates immediately when you set the checked property.

参看

Checkbox.defaultChecked

defaultChecked

A Boolean value indicating the default selection state of a checkbox button.

属性源 Checkbox
实现版本 Navigator 2.0

安全性

Navigator 3.0：该属性默认是带有污点的。有关数据污点的更多信息，请看“JavaScript 的安全性”。

描述

If a checkbox is selected by default, the value of the defaultChecked property is true; otherwise, it is false. defaultChecked initially reflects whether the CHECKED attribute is used within an INPUT tag; however, setting defaultChecked overrides the CHECKED attribute.

You can set the defaultChecked property at any time. The display of the checkbox does not update when you set the defaultChecked property, only when you set the checked property.

参看

Checkbox.checked

form

An object reference specifying the form containing the checkbox.

属性源 Checkbox
只读
实现版本 Navigator 2.0

描述

每个表单元素都有一个 form 属性用于指向元素的父表单。该属性在事件控制句柄中特别有用，你可能想要由其获得当前表单中其它元素。

参看

Form

name

A string specifying the checkbox's name.

属性源 Checkbox
实现版本 Navigator 2.0

安全性

Navigator 3.0：该属性默认是带有污点的。有关数据污点的更多信息，请看“JavaScript 的安全性”。

描述

If multiple objects on the same form have the same NAME attribute, an array of the given name is created automatically. Each element in the array represents an individual Form object. Elements are indexed in source order starting at 0. For example, if two Text elements and a Button element on the same form have their NAME attribute set to "myField", an array with the elements myField[0], myField[1], and myField[2] is created. You need to be aware of this situation in your code and know whether myField refers to a single element or to an array of elements.

示例

In the following example, the valueGetter function uses a for loop to iterate over the array of elements on the valueTest form. The msgWindow window displays the names of all the elements on the form:

newWindow=window.open("http://home.netscape.com") function valueGetter() {
   var msgWindow=window.open("")
   for (var i = 0; i < newWindow.document.valueTest.elements.length; i++) {
      msgWindow.document.write(newWindow.document.valueTest.elements[i].name + "<BR>")
   }
}