title: What are the limitations of Opal?
body: <p>I'm very keen to try <a href="http://opalrb.com/" rel="nofollow noreferrer">Opal</a> in a new Rails project, but the risk of course is that I won't discover what it <em>can't</em> do until I've spent hundreds of hours doing everything else, and run into a brick wall that I can't possibly get through.</p>
  
  <p>What are its limitations?</p>
  
  <p>For example (and of course answers should not be limited to these topics if there are other limitations worth mentioning) I would assume that you can't just use any old Ruby library in your Opal code (but I'd love to find out that I'm wrong about that!).</p>
  
  <p>I would also guess there might be difficulties in using any arbitrary JavaScript library, or that there are cases where you need to write JavaScript to interface with those.</p>
  
  <p>And of course there could be all sorts of issues that I haven't even begun to imagine.  It looks like an amazing project, but I want to know what gotchas I might encounter unexpectedly if I were to just dive in head-first.</p>