Script Tags from localhost? by jahbrewski

I cannot get Script Tags to load from localhost:
      ss = ShopifyAPI::ScriptTag.create({:src => "http://localhost:3000/assets/javascripts/modal.js", :event => 'onload'})
However, I got them to load after uploading to AWS:
      ss = ShopifyAPI::ScriptTag.create({:src => "https://s3.amazonaws.com/echome/modal.js", :event => 'onload'})
This doesn't work well for development though -- I need to load the scripts to AWS every time I make changes. What am I missing here? There must be a better way.