title: Block JS from loading on certain domains
body: <p>I have a web service that works through giving users javascript to embed in their code. Users can also place that code on other sites to make it work there. However I also need to allow users to create a blacklist of sites that the JS should not function on. For example, a competitor or an inappropriate site. </p>
  
  <p>Is there a way to check where our JS files are being loaded from, and block loading or break functionality on a per account basis? </p>
  
  <p><strong>Edit: The javascript loads an iframe on the site, so another solution would be to somehow block certain domains from loading an iframe from our server, or serve different content to that iframe</strong></p>
  
  <p><strong>Edit 2: We're also trying to avoid doing this from with the JS because it could be downloaded and modified to get pass the block</strong></p>