title: Inspect history in react-router-dom with HashRouter
body: <p>As described in the title, I'm using react-router-dom and HashRouter to serve a client side app in a portion of my site.</p>
  
  <p>What I'm trying to achieve is something like a back button to pop through the history. This is fine in normal situations, but the history seems to contain the entire browser history - so if someone links directly to a page and click the back button, it will take them back to the previous site.</p>
  
  <p>I'd like to be able to detect when this is the case (i.e. the last thing in the history was not within the hash history) - that way I could do something different.</p>
  
  <p>Thanks in advance for the help</p>
  
  <p>Matt</p>