Chapter 21
JavaScript Reference

Form Object

Name

Form Object---an HTML input form

Synopsis

document.form_name
document.forms[form_number]
document.forms.length

Properties

action

A read/write string specifying the URL to which the form is to be submitted. Initially specified by the ACTION attribute.

elements[]

An array of input elements that appear in the form. Each element is a Button, Checkbox, Hidden, Password, Radio, Reset, Select, Submit, Text, or Textarea object.

elements.length

The number of items in the elements[] array.

encoding

A read/write string that specifies the encoding method used for form data. Initially specified by the ENCTYPE attribute. The default encoding of "application/x-www-form-urlencoded" is almost always appropriate.

method

A read/write string that specifies the technique for submitting the form. It should have the value "get" or "post". Initially specified by the METHOD attribute.

target

A read/write string that specifies the name of the frame or window in which the results of submitting a form should be displayed. Initially specified by the TARGET attribute. The special names "_top", "_parent", "_self", and "_blank" are also supported for the target property and the TARGET attribute.

Methods

reset()

Reset each of the input elements of the form to their default values.

submit()

Submit the form.

Event Handlers

onreset()

An event handler invoked just before the elements of the form are reset. Specified by the onReset attribute.

onsubmit()

An event handler that is invoked just before the form is submitted. Specified by the onSubmit attribute. This event handler allows form entries to be validated before being submitted.

HTML Syntax

A Form object is created with a standard HTML <FORM> tag. JavaScript adds the optional onReset and onSubmit event-handler attributes to this tag. The form contains any input elements created with the <INPUT> tag between <FORM> and </FORM>.

<FORM
    [ NAME="form_name" ]  used to name the form in JavaScript
    [ TARGET="window_name" ]  the name of the window for responses
    [ ACTION="url" ]  the URL to which the form is submitted
    [ METHOD=(GET|POST) ]   the method of form submission
    [ ENCTYPE="encoding" ]    how the form data is encoded
    [ onReset="handler" ] a handler invoked when form is reset
    [ onSubmit="handler" ]    a handler invoked when form is submitted
>
    form text and <INPUT> tags go here
</FORM>

Description

The Form object represents an HTML <FORM> in a document. Each form in a document is represented as an element of the Document.forms[] array. Named forms are also represented by the form_name property of their document, where form_name is the name specified in the NAME attribute of the <FORM> tag.

The elements of a form (buttons, input fields, check boxes, and so on) are collected in the Form.elements[] array. Named elements, like named forms, can also be referenced directly by name--the element name is used as a property name of the Form object. Thus, to refer to a Text object element named "phone" within a form named "questionnaire," you might use the JavaScript expression:

document.questionnaire.phone

See the descriptions of the Form properties and methods for more information about this object.