CHECK IF USER IS OFFLINE/ONLINE
Run 
<!doctype html>
	<head>
		<style>
			/* CSS comes here */
			body {
			    padding:10px;
			    font-family:arial;
			    font-size:1.2em;
			}
			.error {
			    background-color:#ff5252;
			    color:white;
			    padding:10px;
			    border-radius:5px;
			    margin-top:10px;
			}
			.success {
			    background-color:#00e676;
			    color:white;
			    padding:10px;
			    border-radius:5px;
			    margin-top:10px;
			}
		</style>
		<title>Check if User is Offline/Online</title>
	</head>
	<body>
		<h2>Welcome to Studytonight!</h2>
        <p>This is a simple code example to show you how to find when a user goes offline and when the user comes back online to show some messages to the user when this happens.</p>
        <div id="status"></div>
		<script>
			/* JS comes here */
			let status = document.getElementById("status");
			
            window.addEventListener('load', function(e) {
                if (navigator.onLine) {
                    status.innerHTML = "User is online";
                    status.classList.add("success");
                } else {
                    status.innerHTML = "User is offline";
                    status.classList.remove("success");
                    status.classList.add("error");
                }
            }, false);
            
            window.addEventListener('online', function(e) {
                status.innerHTML = "User is back online";
                status.classList.remove("error");
                status.classList.add("success");
            }, false);
            
            window.addEventListener('offline', function(e) {
                status.innerHTML = "User went offline";
                status.classList.remove("success");
                status.classList.add("error");
            }, false);
            
		</script>
	</body>
</html>