Availability

JavaScript 1.0; enhanced in JavaScript 1.1

Inherits from/Overrides

Inherits from Input, HTMLElement

Synopsis

form.name
form.elements[i]

Properties

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

value

A read/write string that specifies arbitrary data passed to the web server when the form containing the Hidden object is submitted. The initial value of value is specified by the value attribute of the <input> tag that defines the Hidden object.

HTML Syntax

A Hidden element is created with a standard HTML <input> tag:

<form>
    ...
  <input
    type="hidden"      // Specifies that this is a Hidden element
    [ name="name" ]    // A name you can use later to refer to this element
                       // Specifies the name property
    [ value="value" ]  // The value transmitted when the form is submitted
                       // Specifies the initial value of the value property
  >
    ...
</form> 

Description

The Hidden element is an invisible form element that allows arbitrary data to be transmitted to the server when the form is submitted. You can use a Hidden element when you want to transmit information other than the user's input data to the server.

When an HTML document is generated on the fly by a server, another use of Hidden form elements is to transmit data from the server to the client for later processing by JavaScript on the user's side. For example, the server might transmit raw data to the client in a compact, machine-readable form by specifying the data in the value attribute of a Hidden element or elements. On the client side, a JavaScript program (transmitted along with the data or in another frame) could read the value property of the Hidden element or elements and process, format, and display that data in a less compact, human-readable (and perhaps user-configurable) format.

Hidden elements can also be useful for communication between CGI scripts, even without the intervention of JavaScript on the client side. In this usage, one CGI script generates a dynamic HTML page containing hidden data, which is then submitted to a second CGI script. This hidden data can communicate state information, such as the results of the submission of a previous form.

Cookies can also be used to transmit data from client to server. An important difference between Hidden form elements and cookies, however, is that cookies are persistent on the client side.

See Also

Document.cookie, Form, HTMLElement, Input; HTMLInputElement in the DOM reference section