I found the answer myself!
This happens because rails applies custom ID to forms depending on action. If it is "New" action, then ID would be "new_object". If it is "Edit" action, then class would be "edit_object".
I applied custom class like:
<%= form_for(@deal, html: { "data-abide" => '', id: "deal_form"}, builder: SmartLabelFormBuilder) do |f| %>
...
<% end %>
and
$("#deal_form input").keyup ->
css_klass = $(this).attr("class")
$(this).attr('value', $(this).val())
inpt = $(this).val()
$("." + css_klass + "_preview").html inpt
And it works.