problem in text_field

hello everybody

I have this text_field

<%= f.text_field :precio_compra, {:size=> 10, :onchange => "#{remote_function(:url=>{:controller=> "accions", :action=> "comprueba"},:with => "'valor='+ 'accion[precio_compra]'.value")}"} %></p>

but in comprueba funtion i have this

=> {"authenticity_token"=>"ea3bfcd9b5acd6ffbaf6d4b57850f58fd0dcf734", "valor"=>"undefined", "action"=>"comprueba", "controller"=>"accions"}

valor=> "undefine"

How I pass the text_field value???

Assuming foo was the id of the element you'd want $F('foo') instead of
'accion[precio_compra]'.value which is basically meaningless to
javascript.

Fred