Code Snippet
PageVisibility API
<!DOCTYPE HTML>
<html>
<head>
<script type="text/javascript">
timer = 0;
function onLoad(){
document.addEventListener("visibilitychange",stateChanged);
document.addEventListener("webkitvisibilitychange", stateChanged);
document.addEventListener("msvisibilitychange", stateChanged);
}
function stateChanged(){
console.log(document.webkitVisibilityState);
if(document.hidden || document.webkitHidden || document.msHidden){
//new tab or window minimized
timer = new Date().getTime();
}
else {
alert('You were away for ' + (new Date().getTime()-timer)/1000+ ' seconds.')
}
}
</script>
</head>
<body onLoad="onLoad()">
</body>
</html>
Demo by Sagar Ganatra