observe_field(field_id, options = {}) — ActionView::Helpers::PrototypeHelper

observe_field(field_id, options = {})

Observes the field with the DOM ID specified by field_id and calls a callback when its contents have changed. The default callback is an Ajax call. By default the value of the observed field is sent as a parameter with the Ajax call.

Example:

# Generates: new Form.Element.Observer('suggest', 0.25, function(element, value) {new Ajax.Updater('suggest',
#         '/testing/find_suggestion', {asynchronous:true, evalScripts:true, parameters:'q=' + value})})
<%= observe_field :suggest, :url => { :action => :find_suggestion },
     :frequency => 0.25,
     :update => :suggest,
     :with => 'q'
     %>

Required options are either of:

:url

url_for-style options for the action to call when the field has changed.

:function

Instead of making a remote call to a URL, you can specify javascript code to be called instead. Note that the value of this option is used as the body of the javascript function, a function definition with parameters named element and value will be generated for you for example:

observe_field("glass", :frequency => 1, :function => "alert('Element changed')")

will generate:

new Form.Element.Observer('glass', 1, function(element, value) {alert('Element changed')})

The element parameter is the DOM element being observed, and the value is its value at the time the observer is triggered.

Additional options are:

:frequency

The frequency (in seconds) at which changes to this field will be detected. Not setting this option at all or to a value equal to or less than zero will use event based observation instead of time based observation.

:update

Specifies the DOM ID of the element whose innerHTML should be updated with the XMLHttpRequest response text.

:with

A JavaScript expression specifying the parameters for the XMLHttpRequest. The default is to send the key and value of the observed field. Any custom expressions should return a valid URL query string. The value of the field is stored in the JavaScript variable value.

Examples

:with => "'my_custom_key=' + value"
:with => "'person[name]=' + prompt('New name')"
:with => "Form.Element.serialize('other-field')"

Finally

:with => 'name'

is shorthand for

:with => "'name=' + value"

This essentially just changes the key of the parameter.

Additionally, you may specify any of the options documented in the Common options section at the top of this document.

Example:

# Sends params: {:title => 'Title of the book'} when the book_title input
# field is changed.
observe_field 'book_title',
  :url => 'http://example.com/books/edit/1',
  :with => 'title'

Parameters

field_id req
options opt = {}

Source

# File actionpack/lib/action_view/helpers/prototype_helper.rb, line 547
      def observe_field(field_id, options = {})
        if options[:frequency] && options[:frequency] > 0
          build_observer('Form.Element.Observer', field_id, options)
        else
          build_observer('Form.Element.EventObserver', field_id, options)
        end
      end

Defined in actionpack/lib/action_view/helpers/prototype_helper.rb line 547 · View on GitHub · Improve this page · Find usages on GitHub

Defined in ActionView::Helpers::PrototypeHelper

Signature

Parameters