Listen for visibilitychange, instead of unload/beforeunload about autotrack HOT 5 CLOSED

var
  VisibilityStates = {
    prerender: 'prerender'
    ,visible: 'visible'
    ,hidden: 'hidden'
  }
  ,VisibilityState = VisibilityStates.visible // dont want to deal with prerender
  ,visibilityCallbacks = {
    visible: []
    ,hidden: []
  }
;
function onForeground(event) {
  processVisibilityChange('visible', event)
}
function onBackground(event) {
  processVisibilityChange('hidden', event)
}
function onVisibilityChange(event) {
  processVisibilityChange(document.visibilityState, event)
}
function processVisibilityChange(newState, event) {
  // console.log("VisibilityState: " + VisibilityState + ' -> ' + VisibilityStates[newState], event)
  // ignore prerender
  if (newState == 'prerender') return;
  // ignore unless changed
  if (VisibilityState == VisibilityStates[newState]) return;
  // fire callbacks
  VisibilityState = VisibilityStates[newState];
  var i, cbs = visibilityCallbacks[newState];
  for (i = 0; i < cbs.length; i++) { cbs[i].call(event) }
}
window.addEventListener("beforeunload", onBackground, false);
window.addEventListener("pagehide", onBackground, false);
window.addEventListener("pageshow", onForeground, false);
if (document.visibilityState) document.addEventListener("visibilitychange", onVisibilityChange, false);

visibilityCallbacks.visible.push(function(){
  ga('set', 'page', window.location.href);
  ga('send', 'pageview');
});