Javascript [Electronic resources] : The Definitive Guide (4th Edition) نسخه متنی

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JavaScript
1.0; enhanced in JavaScript 1.1

Inherits from/Overrides

Inherits from HTMLElement

Synopsis

form.elements[i]
form.name

Properties

Input
inherits properties from HTMLElement and defines or overrides the
following:

checked

A read/write boolean that specifies whether a Checkbox or Radio form
element is currently checked. You can set the state of these button
elements by setting the value of this property. This property is not
used by other form elements.

defaultChecked

A read-only boolean value that specifies whether a Checkbox or Radio
element is checked by default. This property is used to restore the
Checkbox or Radio element to its default value when the form is reset
and has no meaning for other form elements.
defaultChecked corresponds to the
checked attribute in the HTML
<input> tag that created the form element.
If checked was present,
defaultChecked is true.
Otherwise, defaultChecked is
false.

defaultValue

Specifies the initial text that appears in the form element and the
value that is restored to that element when the form is reset. This
property is used only by the Text, Textarea, and Password elements.
For security reasons, it is not used by the FileUpload element. For
Checkbox and Radio elements, the equivalent property is
defaultChecked.

form

A read-only reference to the Form
object that contains the element. The form
property allows the event handlers of one form element to easily
refer to sibling elements in the same form. When an event handler is
invoked, the this keyword refers to the form
element for which it was invoked. Thus, an event handler can use the
expression this.form to refer to the form that
contains it. From there, it can refer to sibling elements by name or
use the elements[] array of the Form object to
refer to them by number.

length

For the Select form element, this property specifies the number of
options or choices (each represented by an Option object) that are
contained within the options[] array of the
element. See the Select reference page.

name

A read-only string, specified by the HTML name
attribute, that specifies the name of this element. This name may be
used to refer to the element, as shown in the preceding
Input.name
reference page.

options[]

For the Select form element, this array contains Option objects that
represent the options or choices displayed by the Select object. The
number of elements in the array is specified by the
length property of the Select element. See the
Input.name reference page.

selectedIndex

For the Select form element, this integer specifies which option
displayed by the Select object is currently selected. In JavaScript
1.1, this property is read/write. In JavaScript 1.0, it is read-only.
See the Input.name reference page.

type [ JavaScript 1.1]

A read-only string that specifies the type of the form element. See
the Input.type reference page.

value

A string that specifies the value displayed by the element and/or to
be sent to the server for this element when the form that contains it
is submitted. See the Input.value reference page.

Methods

Input inherits methods from HTMLElement and defines or overrides the
following:

blur( )

Removes keyboard focus from the element.

click( )

Simulates a mouse-click on the form element.

focus( )

Gives keyboard focus to the element.

select( )

For form elements that display editable text, selects the text that
appears in the element.

Event Handlers

Input inherits event handlers from HTMLElement and defines or
overrides the following:

onblur

Invoked when the user takes keyboard focus away from the element.

onchange

For form elements that are not buttons, this event handler is invoked
when the user enters or selects a new value.

onclick

For form elements that are buttons, this event handler is invoked
when the user clicks or selects the button.

onfocus

Invoked when the user gives keyboard focus to the element.

Description

Form elements are stored in the elements[] array
of the Form object. The contents of this array are Input objects,
which represent the individual buttons, input fields, and other
controls that appear within the form. Many types of input elements
are created with the <input> tag; others are
created with the <select> and
<option> tags and the
<textarea> tag. The various form input
elements share quite a few properties, methods, and event handlers,
which are described on this reference page. Specific behaviors for
specific types of form elements are described on their own pages.

The Input object defines many shared properties, methods, and event
handlers, but not all of them are shared by all types of form
elements. For example, the Button object triggers the
onclick event handler but not the
onchange handler, while the Text object triggers
onchange but not onclick. The
following figure shows all of the form elements and the properties
associated with them.

There are two broad categories of form elements. The first is the
buttons: Button, Checkbox, Radio, Reset, and Submit. These elements
have an onclick event handler but not an
onchange handler. Similarly, they respond to the
click( ) method but not to the select(
) method. The second category contains those elements that
display text: Text, Textarea, Password, and FileUpload. These
elements have an onchange event handler rather
than an onclick handler, and they respond to the
select( ) method but not to the click(
) method.

The Select element is a special case. It is created with the
<select> tag and is less like the
<input> elements than the other form
elements. Although the Select element is technically represented by a
different object type, it is still convenient to consider it an Input
object.

See Also

Button, Checkbox, FileUpload, Form, Hidden, Password, Radio, Reset,
Select, Submit, Text, Textarea; Chapter 15;
HTMLInputElement in the DOM reference section