Rails 3 - custom ajax action is not working - ruby

Question

I want to create a custom action in Rails which will update views and print some info on div.
I use that gem for file upload:
https://github.com/valums/file-uploader/blob/master/client/fileuploader.js
After successful upload I want to update with ajax page how many miliseconds it takes.
In old Rails I would write that with:
def set_tab
#diff = count_miliseconds_method
render :update do |page|
page.replace_html "place_menu", render( :partial => 'place_menu')
end
end
But I cant figure out how to do that in Rails 3.1.
My custom action controller code:
def custom
[...] # Here everything works OK
start_time = Time.now
Some_method
end_time = Time.now
#diff = ((end_time - start_time)*100).to_i # counted miliseconds
respond_to do |format|
format.json {render :json => {:success => true, :time => #diff}, :status => :created, :location => custom_words_path}
end
end
My custom.js.erb code
var el = $('#upload-log');
el.append("#{#diff} ms");
Unfortunately this doesnt work. I get response e.g.
{"success":true, "time":324}
but js.erb file doesnt get executed and page doesnt containt information about miliseconds.
Any idea how to fix that?
Update
Github repo:
https://github.com/there-is-no-spoon/Anagram

Answer 1

To execute js.erb file you have to pass
:format => :js
to your path generating method - for example:
link_to "My custom action", my_action_path(:format => :js)

Answer 2

You're returning JSON now (in Rails 3.1) not a chunk of string containing Javascript (as was the case before).
You need to write your code which handles your result where you make the Ajax Call. I assume you're using jQuery. So where you make the Ajax call, implement the success handler and do the
var el = $("#upload-log");
...
stuff there.
Basically server does not return Javascript anymore, it is completely on the client side only.
You need to implement the onComplete method of your file upload plugin. Read the manual of your js plugin, its mentioned clearly.