 <p>The problem is as others in the comments mentioned, that your javascript resource is not precompiled.</p> <p>The solution is a little bit more than just making sure you precompile the assets, which by the way heroku will do when you push so you don't have to.</p> <p>The problem lies in that you are doing this:</p> <pre><code>&lt;% content_for :script do %&gt; &lt;%= javascript_include_tag 'hover_content' %&gt; &lt;% end %&gt; </code></pre> <p>Since you are referencing hover_content directly instead of just including it in your application.js then you must tell Rails that you want this included in the asset precompile step.</p> <p>Modify your production.rb file and add this line:</p> <pre><code>config.assets.precompile += %w( hover_content.js ) </code></pre> <p>That will tell rails that in addition to the application.js which automatically gets compiled and included that you want to also include this other file hover_content.js</p>