# Use observe\_field within form\_tag

**URL:** <https://www.ruby-forum.com/t/use-observe-field-within-form-tag/173573>\
**Category:** Rails\
**Created:** [August 11, 2009, 4:13pm UTC](https://www.ruby-forum.com/t/use-observe-field-within-form-tag/173573 "2009-08-11T16:13:14Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![iggar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/a88e57/32.png) [@iggar](https://www.ruby-forum.com/u/iggar)\
**Post date:** [August 11, 2009, 4:13pm UTC](https://www.ruby-forum.com/t/use-observe-field-within-form-tag/173573/1 "2009-08-11T16:13:14Z")

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Hey,

I’m trying to observe a field that is inside a form\_tag like so:

\<% form\_tag ‘send\_mail’ do %\>  
\<%= select\_tag ‘select\_club’,  
options\_from\_collection\_for\_select(clubs,‘id’,‘name’), :class =\>  
‘ComboBox’ %\>

\<%= observe\_field ‘select\_club’,:url=\>{:action =\> ‘clubs\_changed’} %\>  
\<% end %\>

When I run this in FireFox gives me the following JavaScript error:  
Form is not defined  
and then points to the generated javascript:  
new Form.Element.EventObserver(‘select\_club’, function(element, value)  
{new Ajax.Request(’/mailings/clubs\_changed’, {asynchronous:true,  
evalScripts:true, parameters:value + ‘&authenticity\_token=’ +  
encodeURIComponent(‘06f49bb619c38f8d0ea988932e4324abbd8511ef’)})})

My html does contain a form so I don’t exactly know where to look  
anymore.

Thanks!

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<div class="post-metadata">

**Author:** ![iggar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/a88e57/32.png) [@iggar](https://www.ruby-forum.com/u/iggar)\
**Post date:** [August 11, 2009, 4:15pm UTC](https://www.ruby-forum.com/t/use-observe-field-within-form-tag/173573/2 "2009-08-11T16:15:47Z")

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refer

> **[observe\_field Example - Ruby on Rails](http://blogofchirag.blogspot.com/2008/09/observefield-example-ruby-on-rails.html)**
>
> Live Book Search: \<%= text\_field\_tag :search...

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<div class="post-metadata">

**Author:** ![iggar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/a88e57/32.png) [@iggar](https://www.ruby-forum.com/u/iggar)\
**Post date:** [August 11, 2009, 4:21pm UTC](https://www.ruby-forum.com/t/use-observe-field-within-form-tag/173573/3 "2009-08-11T16:21:26Z")

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Wap A. wrote:

> refer  
> [Web Professional: observe\_field Example - Ruby on Rails](http://blogofchirag.blogspot.com/2008/09/observefield-example-ruby-on-rails.html)

This doesn’t really help me.  
The link doesn’t even use a form\_tag.