title: setInterval and long running functions
body: <p>How does setInterval handle callback functions that take longer than the desired interval?</p>
  
  <p>I've read that the callback may receive the number of milliseconds late as its first argument, but I was unable to find why it would be late (jitter, or long running functions).</p>
  
  <p>And the wonderful follow up, does it behave differently for the common browsers?</p>