title: how to have onchange in collection_select with jquery
body: <p>I am using jquery on my html page and want to have an onchange event on a collection_select. </p>
  
  <p>If I add <code>&lt;%= javascript_include_tag :defaults %&gt;</code> then my jquery code does not work. </p>
  
  <p>Basically I have a collection_select as follows:</p>
  
  <pre><code>&lt;%=collection_select(:product, 'prod_name', @prods, :id, :prod_name, 
  {:prompt =&gt; 'Select Product'},{:onchange =&gt;  remote_function(:url =&gt; 
  {:action =&gt; 'volume_or_quant'}, :with =&gt; "'id=' + this.value")})%&gt;
  </code></pre>
  
  <p>Then I have a select tag and a text field:</p>
  
  <pre><code>&lt;%=select_tag :volume, options_for_select(["", "1/8 lb", "1/4 lb", "Single", 
  "Multi 5" ], "N/A") %&gt;
  &lt;%= text_field_tag :quantity, "", :size=&gt;"4"%&gt;
  </code></pre>
  
  <p>When an option is selected from the <code>collection_select</code> I want to go back to my action and check whether it has volume or unit in the DB. Based on which, the above selectbox/textbox will be enabled. </p>
  
  <p>right now my action looks like: </p>
  
  <pre><code>def volume_or_quant
      @product = Product.find(params[:id])
      puts "Value: " + @product.volume        
  end
  </code></pre>
  
  <p>However, when I select something...nothing happens. Right now I do not have default javascripts. </p>
  
  <p>is what I'm trying to do require the default prototype javascript? or can it be done with jquery?</p>