How do I load pop up box in a JS Rails response?

I have a controller that responds to JS queries:

def show
@event = Event.find(params[:id]) 
respond_to do |format|
format.js
end
end 

My show.js.erb:

$("#modal").html("<%= escape_javascript(render(:partial => @event)) %>");
$('#modal').dialog();

I want to render partial details into pop-up box. In here modal is my hidden div and when I run this code I get some errors and js.erb file run as plain html which having js.erb content.

element.dispatchEvent is not a function

element.tagName is undefined

What is the reason for this? How can I load pop-up box?

I think you might be missing the partial name? Have you tried (assume the partial is called _widget.html.erb):

escape_javascript(render(:partial => 'widget', :locals => {:event => @event}))