title: setInterval stops without any reason when browser tab is background
body: <p>I am working on an application that sends current timestamp to database every 2 minutes with AJAX using setInterval.</p>
  
  <p>But somehow setInterval stops after some minutes (i didnt calculate the exact time), but i believe it happens when i dont open that browser's tab for 20-30 minutes.</p>
  
  <pre><code>function tmstmp() {
  $.post("send_functions.php?act=time");
  }
  
  $(function() { 
  setInterval(tmstmp, 60000);
  });
  </code></pre>
  
  <p>Is that normal that setInterval stops if that tab is not on foreground ?</p>
  
  <p>If yes, how can i prevent setInterval to stop ? or check if it stopped ?</p>
  
  <p>Thanks </p>