Time On Visible and Hidden Page

Visible&HiddenTimeOnPage

<script>
  
 (function(){
  // Initialize time 
  var startTime = new Date().getTime();
  var totalTime = {};
  if (typeof prefix() !== 'undefined') {
  var prevTime = 0;
  var visibilityEvent = prefix() + 'visibilitychange';
  var tabPath = 'visibleTab';
    
//Initialize the listeners
document.addEventListener(visibilityEvent,        
function(e){
  var isHidden=visibilityState(prefix())
  if (typeof isHidden !== 'undefined') {
  prevTime = 0 ? new Date().getTime() - startTime : new Date().getTime() - startTime - prevTime;  
  
    //Total Time for previous visibility state 
    if(isHidden) { totalTime.visibleTime=prevTime; tabPath+=">hiddenTab"} 
     else {totalTime.hiddenTime=prevTime; tabPath+=">visibleTab" } 
    }  
         //////Debugging Datalayer Event ///////// 
              dataLayer.push({
              'event' : 'visibilityChange',
              'visibleTime' : totalTime.visibleTime,
              'hiddenTime': totalTime.hiddenTime,
              'hidden' : isHidden,
              'tabPath': tabPath  
            });
         /////////////// 
}, false);
    
window.addEventListener('beforeunload', function(e)  
{
var isHidden=visibilityState(prefix())

if (typeof isHidden !== 'undefined') {
prevTime = 0 ? new Date().getTime() - startTime : new Date().getTime() - startTime - prevTime;  
if(!isHidden){totalTime.visibleTime=prevTime} 
else {totalTime.hiddenTime=prevTime} 
}  

if(tabPath.split('>').length > 3) {
var len = Math.floor(tabPath.split('>').length / 2);
var adtxt = ''
if(tabPath.split('>').length / 2 % 1 !== 0){adtxt+=' > visibleTab';}
tabPath = '(visibleTab > hiddenTab) x '+len+adtxt
}
  
dataLayer.push({
'event' : 'sendTimings',
'visibleTime' : totalTime.visibleTime,
'hiddenTime': totalTime.hiddenTime,
'hidden' : isHidden,
'tabPath': tabPath
}); 
  
  // reset the variables after sending data to analytics  
  prevTime=0;
  startTime = new Date().getTime();
  totalTime = {};
  tabPath = 'visibleTab';
}, false);

}
 })()
  
  function prefix() {
  var prefixes = ['moz', 'ms', 'o', 'webkit'];
  
    if ('hidden' in document) {
    return '';
  }
  
   // Loop through each prefix to see if it is supported. 
  for (var i = 0; i < prefixes.length; i++) {
    var testPrefix = prefixes[i] + 'Hidden';
    if (testPrefix in document) {
      return prefixes[i];
    }
  }

  return;
}

 function visibilityState(pref){
    switch (pref) {
    case '':
      return document['hidden'];
    case 'moz':
      return document['mozHidden'];
    case 'o':
      return document['oHidden'];
    case 'webkit':
      return document['webkitHidden'];
    default:
      return;
  }
}
    
  
</script>