“respond_to do |format|” throws UnknownFormat error

Question

I'm trying to render a js file from a controller with ajax. This exact code always worked before, and it even works in other methods, but I suddenly started getting this error:

ActionController::UnknownFormat in MoviesController#vote
ActionController::UnknownFormat

Movies Controller:

def vote
  ...
  respond_to do |format| #The error points to this line.
    format.js
  end
end

vote.js.erb:

$('#votes').html("<%= escape_javascript(render 'votes') %>");

The link:

movies.html.erb:

<%= render 'votes' %>

_votes.html.erb

<%= link_to "vote", vote_path, method: :post, remote: true %>

routes.rb:

post 'movies/vote' => 'movies#vote', as: 'vote'

Why am I suddenly getting this error? Why does it work in different contexts but not in this one?

Using Rails 4.0.10

UPDATE: Stack Trace

Application Trace:

app/controllers/movies_controller.rb:394:in `vote'

Full Trace:

actionpack (4.0.10) lib/action_controller/metal/mime_responds.rb:372:in `retrieve_collector_from_mimes'
actionpack (4.0.10) lib/action_controller/metal/mime_responds.rb:189:in `respond_to'
app/controllers/movies_controller.rb:394:in `vote'
actionpack (4.0.10) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (4.0.10) lib/abstract_controller/base.rb:189:in `process_action'
actionpack (4.0.10) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (4.0.10) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (4.0.10) lib/active_support/callbacks.rb:413:in `_run__1492335060096380544__process_action__callbacks'
activesupport (4.0.10) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.10) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (4.0.10) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (4.0.10) lib/action_controller/metal/instrumentation.rb:31:in `block in process_action'
activesupport (4.0.10) lib/active_support/notifications.rb:159:in `block in instrument'
activesupport (4.0.10) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.0.10) lib/active_support/notifications.rb:159:in `instrument'
actionpack (4.0.10) lib/action_controller/metal/instrumentation.rb:30:in `process_action'
actionpack (4.0.10) lib/action_controller/metal/params_wrapper.rb:250:in `process_action'
activerecord (4.0.10) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (4.0.10) lib/abstract_controller/base.rb:136:in `process'
actionpack (4.0.10) lib/abstract_controller/rendering.rb:44:in `process'
actionpack (4.0.10) lib/action_controller/metal.rb:195:in `dispatch'
actionpack (4.0.10) lib/action_controller/metal/rack_delegation.rb:13:in `dispatch'
actionpack (4.0.10) lib/action_controller/metal.rb:231:in `block in action'
actionpack (4.0.10) lib/action_dispatch/routing/route_set.rb:82:in `call'
actionpack (4.0.10) lib/action_dispatch/routing/route_set.rb:82:in `dispatch'
actionpack (4.0.10) lib/action_dispatch/routing/route_set.rb:50:in `call'
actionpack (4.0.10) lib/action_dispatch/journey/router.rb:71:in `block in call'
actionpack (4.0.10) lib/action_dispatch/journey/router.rb:59:in `each'
actionpack (4.0.10) lib/action_dispatch/journey/router.rb:59:in `call'
actionpack (4.0.10) lib/action_dispatch/routing/route_set.rb:676:in `call'
warden (1.2.3) lib/warden/manager.rb:35:in `block in call'
warden (1.2.3) lib/warden/manager.rb:34:in `catch'
warden (1.2.3) lib/warden/manager.rb:34:in `call'
rack (1.5.5) lib/rack/etag.rb:23:in `call'
rack (1.5.5) lib/rack/conditionalget.rb:25:in `call'
rack (1.5.5) lib/rack/head.rb:11:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/params_parser.rb:27:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/flash.rb:241:in `call'
rack (1.5.5) lib/rack/session/abstract/id.rb:225:in `context'
rack (1.5.5) lib/rack/session/abstract/id.rb:220:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/cookies.rb:486:in `call'
activerecord (4.0.10) lib/active_record/query_cache.rb:36:in `call'
activerecord (4.0.10) lib/active_record/connection_adapters/abstract/connection_pool.rb:626:in `call'
activerecord (4.0.10) lib/active_record/migration.rb:373:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (4.0.10) lib/active_support/callbacks.rb:373:in `_run__2656547782179467807__call__callbacks'
activesupport (4.0.10) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.10) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/reloader.rb:64:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/remote_ip.rb:76:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
web-console (2.2.1) lib/web_console/middleware.rb:39:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
railties (4.0.10) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.0.10) lib/rails/rack/logger.rb:20:in `block in call'
activesupport (4.0.10) lib/active_support/tagged_logging.rb:68:in `block in tagged'
activesupport (4.0.10) lib/active_support/tagged_logging.rb:26:in `tagged'
activesupport (4.0.10) lib/active_support/tagged_logging.rb:68:in `tagged'
railties (4.0.10) lib/rails/rack/logger.rb:20:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/request_id.rb:21:in `call'
rack (1.5.5) lib/rack/methodoverride.rb:21:in `call'
rack (1.5.5) lib/rack/runtime.rb:17:in `call'
activesupport (4.0.10) lib/active_support/cache/strategy/local_cache.rb:83:in `call'
rack (1.5.5) lib/rack/lock.rb:17:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/static.rb:64:in `call'
rack (1.5.5) lib/rack/sendfile.rb:112:in `call'
railties (4.0.10) lib/rails/engine.rb:511:in `call'
railties (4.0.10) lib/rails/application.rb:97:in `call'
rack (1.5.5) lib/rack/lock.rb:17:in `call'
rack (1.5.5) lib/rack/content_length.rb:14:in `call'
rack (1.5.5) lib/rack/handler/webrick.rb:60:in `service'
/home/greg/.rvm/rubies/ruby-2.0.0-p648/lib/ruby/2.0.0/webrick/httpserver.rb:138:in `service'
/home/greg/.rvm/rubies/ruby-2.0.0-p648/lib/ruby/2.0.0/webrick/httpserver.rb:94:in `run'
/home/greg/.rvm/rubies/ruby-2.0.0-p648/lib/ruby/2.0.0/webrick/server.rb:295:in `block in start_thread'

Answer 1

You can specify the format option for the route helper to instruct the link to be js instead of the default html . Specify it like this:

<%= link_to "vote", vote_path(format: :js), method: :post, remote: true %>

I've had issues getting that to work with some versions of Rails in the past, but I only have anecdotal evidence about that. What I found does work in that circumstance is this:

<%= link_to "vote", "#{vote_path}.js", method: :post, remote: true %>

In the 2nd case, you simply append the .js extension to the url path that will trigger the js format. Inelegant and brute force, only to be used AFTER unsuccessfully trying the right way, but it does work.

Answer 2

try :

def vote
    respond_to do |format|
      if @comment.update(comment_params)
        format.js {render nothing: true}
        format.json { render :show, status: :ok, location: @comment }
      else
        format.html { render :edit }
        format.json { render json: @comment.errors, status: :unprocessable_entity }
      end
    end
  end

if statement is run successfully like @comment.update(comment_params), comment is update successfully then it execute formate.js, but if it fails due to some reason then it find else render statement. If it not present, it gives Unknown formate error.