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# Hidden

A `Text` object that is suppressed from form display on an HTML form. A `Hidden` object is used for passing name/value pairs when a form submits.

Client-side object |
Implemented in | JavaScript 1.0 JavaScript 1.1: added `type` property

#### Created by

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

#### Description

A `Hidden` object is a form element and must be defined within a `FORM` tag. A `Hidden` object cannot be seen or modified by an end user, but you can programmatically change the value of the object by changing its `value` property. You can use `Hidden` objects for client/server communication.

#### Property Summary

Property | Description
--- | ---

    form

Specifies the form containing the `Hidden` object.

    name

Reflects the `NAME` attribute.

    type

Reflects the `TYPE` attribute.

    value

Reflects the current value of the `Hidden` object.

#### Method Summary

This object inherits the `watch` and `unwatch` methods from `Object`.

#### Examples

The following example uses a `Hidden` object to store the value of the last object the user clicked. The form contains a "Display hidden value" button that the user can click to display the value of the `Hidden` object in an Alert dialog box.

    <HTML>
    <HEAD>
    <TITLE>Hidden object example</TITLE>
    </HEAD>
    <BODY>
    <B>Click some of these objects, then click the "Display value" button
    <BR>to see the value of the last object clicked.</B>
    <FORM NAME="myForm">
    <INPUT TYPE="hidden" NAME="hiddenObject" VALUE="None">
    <P>
    <INPUT TYPE="button" VALUE="Click me" NAME="button1"
       onClick="document.myForm.hiddenObject.value=this.value">
    <P>
    <INPUT TYPE="radio" NAME="musicChoice" VALUE="soul-and-r&b"
       onClick="document.myForm.hiddenObject.value=this.value"> Soul and R&B
    <INPUT TYPE="radio" NAME="musicChoice" VALUE="jazz"
       onClick="document.myForm.hiddenObject.value=this.value"> Jazz
    <INPUT TYPE="radio" NAME="musicChoice" VALUE="classical"
       onClick="document.myForm.hiddenObject.value=this.value"> Classical
    <P>
    <SELECT NAME="music_type_single"
       onFocus="document.myForm.hiddenObject.value=this.options[this.selectedIndex].text">
       <OPTION SELECTED> Red <OPTION> Orange <OPTION> Yellow
    </SELECT>
    <P><INPUT TYPE="button" VALUE="Display hidden value" NAME="button2"
       onClick="alert('Last object clicked: ' + document.myForm.hiddenObject.value)">
    </FORM>
    </BODY>
    </HTML>

#### See also

`document.cookie`

## form

An object reference specifying the form containing this object.

Property of | `Hidden`
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.

#### Examples

Example 1. In the following example, the form `myForm` contains a `Hidden` object and a button. When the user clicks the button, the value of the `Hidden` object is set to the form's name. The button's `onClick` event handler uses `this.form` to refer to the parent form, `myForm`.

    <FORM NAME="myForm">
    Form name:<INPUT TYPE="hidden" NAME="h1" VALUE="Beluga">
    <P>
    <INPUT NAME="button1" TYPE="button" VALUE="Store Form Name"
       onClick="this.form.h1.value=this.form.name">
    </FORM>

Example 2. The following example uses an object reference, rather than the `this` keyword, to refer to a form. The code returns a reference to `myForm`, which is a form containing `myHiddenObject`.

    document.myForm.myHiddenObject.form

#### See also

`Hidden`

## name

A string specifying the name of this object.

Property of | `Hidden`
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.

## type

For all `Hidden` objects, the value of the `type` property is `"hidden"`. This property specifies the form element's type.

Property of | `Hidden`
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.myForm.elements.length; i++) {
       document.writeln("<BR>type is " + document.myForm.elements[i].type)
    }

## value

A string that reflects the `VALUE` attribute of the object.

Property of | `Hidden`
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.

#### Examples

The following function evaluates the `value` property of a group of buttons and displays it in the `msgWindow` window:

    function valueGetter() {
       var msgWindow=window.open("")
       msgWindow.document.write("The submit button says " +
          document.valueTest.submitButton.value + "<BR>")
       msgWindow.document.write("The reset button says " +
          document.valueTest.resetButton.value + "<BR>")
       msgWindow.document.write("The hidden field says " +
          document.valueTest.hiddenField.value + "<BR>")
       msgWindow.document.close()
    }

This example displays the following values:

    The submit button says Query Submit
    The reset button says Reset
    The hidden field says pipefish are cute.

The previous example assumes the buttons have been defined as follows:

    <INPUT TYPE="submit" NAME="submitButton">
    <INPUT TYPE="reset" NAME="resetButton">
    <INPUT TYPE="hidden" NAME="hiddenField" VALUE="pipefish are cute.">

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Last Updated: 05/28/99 11:59:34

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