When you use something like $('#change_email_form').toggle(300); and it gets included twice on the same page, everything doesn’t seem to work as expected…

I ran into this problem when setting up a staging environment using capistrano. My capfile had the usual load 'deploy/assets' which precompiles assets on both production and staging. And everything in production worked fine, but staging not so much. After a few failed attemps I found a fix for the problem.

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config.assets.compile = false

Ruby guides has this to say about assets.compile:

In some circumstances you may wish to use live compilation. In this mode all requests for assets in the pipeline are handled by Sprockets directly. On the first request the assets are compiled and cached as outlined in development above, and the manifest names used in the helpers are altered to include the MD5 hash.

So basically capistrano was compiling the assets and throwing them in public/assets and at the same time Sprockets was trying to handle the requests by using the app/assets directory and all the javascript was included twice. In this case it was both in our subscribe.js and our application.js.

By setting config.assets.compile = false you tell Sprockets to stop attempting to serve your app/assets and solely use your public assets.

This is my final configuration for assets in config/environments/staging.rb

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# Disable Rails's static asset server (Apache or nginx will already do this)
config.serve_static_assets = false
# Don't fallback to assets pipeline if a precompiled asset is missed
config.assets.compile = false
# Generate digests for assets URLs
config.assets.digest = true
# Expands the lines which load the assets
config.assets.debug = true