title: in html, window.onpopstate fires both on loading and on back arrow - how to know?
body: <p>on my page, I have a listener on <code>window.onpopstate</code></p>
  
  <p>I wish to trap the user's back arrow and run my own routine</p>
  
  <p>but <code>window.onpopstate</code> fires when 1) the page is initially loaded, 2) is reloaded, as well as when 3) user presses the back arrow</p>
  
  <p>I <em>could</em> create a state space flag and check it.  but more natural would be to determine from the event itself what's going on.</p>
  
  <p>is there anything intrinsic way to determine whether the event was fired from loading or back button?  when I inspect the two events, they look pretty much the same.</p>