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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

- `onBlur`
- `onClick`
- `onFocus`

#### 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: 05/28/99 11:59:07

Copyright (c) 1999 Netscape Communications Corporation