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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.

Client-side object

Implemented in

JavaScript 1.0

JavaScript 1.1: added type property; added onBlur and onFocus event handlers; added blur and focus methods.

JavaScript 1.2: added handleEvent method.

Created by

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.

Event handlers

Description

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.

Property Summary

Property Description
checked

Boolean property that reflects the current state of the checkbox.

defaultChecked

Boolean property 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.

Method Summary

Method Description
blur

Removes focus from the checkbox.

click

Simulates a mouse-click on the checkbox.

focus

Gives focus to the checkbox.

handleEvent

Invokes the handler for the specified event.

In addition, this object inherits the watch and unwatch methods from Object.

Examples

Example 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
Example 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>

See also

Form, Radio


blur

Removes focus from the checkbox.

Method of

Checkbox

Implemented in

JavaScript 1.0

Syntax

blur()

Parameters

None

See also

Checkbox.focus


checked

A Boolean value specifying the selection state of the checkbox.

Property of

Checkbox

Implemented in

JavaScript 1.0

Security

JavaScript 1.1: This property is tainted by default. For information on data tainting, see the Client-Side JavaScript Guide.

Description

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.

See also

Checkbox.defaultChecked


click

Simulates a mouse-click on the checkbox, but does not trigger its onClick event handler. The method checks the checkbox and sets toggles its value.

Method of

Checkbox

Implemented in

JavaScript 1.0

Syntax

click()

Parameters

None.

Examples

The following example toggles the selection status of the newAge checkbox on the musicForm form:

document.musicForm.newAge.click()

defaultChecked

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

Property of

Checkbox

Implemented in

JavaScript 1.0

Security

JavaScript 1.1: This property is tainted by default. For information on data tainting, see the Client-Side JavaScript Guide.

Description

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.

See also

Checkbox.checked


focus

Gives focus to the checkbox.

Method of

Checkbox

Implemented in

JavaScript 1.0

Syntax

focus()

Parameters

None

Description

Use the focus method to navigate to a the checkbox and give it focus. The user can then toggle the state of the checkbox.

See also

Checkbox.blur


form

An object reference specifying the form containing the checkbox.

Property of

Checkbox

Read-only

Implemented in

JavaScript 1.0

Description

Each form element has a form property that is a reference to the element's parent form. This property is especially useful in event handlers, where you might need to refer to another element on the current form.

See also

Form


handleEvent

Invokes the handler for the specified event.

Method of

Checkbox

Implemented in

JavaScript 1.2

Syntax

handleEvent(event)

Parameters

event

The name of an event for which the specified object has an event handler.


name

A string specifying the checkbox's name.

Property of

Checkbox

Implemented in

JavaScript 1.0

Security

JavaScript 1.1: This property is tainted by default. For information on data tainting, see the Client-Side JavaScript Guide.

Description

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.

Examples

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>")
   }
}

type

For all Checkbox objects, the value of the type property is "checkbox". This property specifies the form element's type.

Property of

Checkbox

Read-only

Implemented in

JavaScript 1.1

Examples

The following example writes the value of the type property for every element on a form.

for (var i = 0; i < document.form1.elements.length; i++) {
   document.writeln("<BR>type is " + document.form1.elements[i].type)
}

value

A string that reflects the VALUE attribute of the checkbox.

Property of

Checkbox

Implemented in

JavaScript 1.0

Security

JavaScript 1.1: This property is tainted by default. For information on data tainting, see the Client-Side JavaScript Guide.

See also

Checkbox.checked, Checkbox.defaultChecked


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Last Updated: 11/16/98 12:56:06

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