HTML 5 Online and offline events

HTML

<header>
    

     <h2 id="status"></h2>

</header>

CSS

body {
    font-family: Segoe UI;
    font-size: 9pt;
}
h1 {
    font-family: Segoe UI;
    font-weight: lighter;
    /*background-color: rgb(27, 161, 226);*/
    color: #fff;
    padding: 20px;
}
h2 {
    color: #fff;
    font-family: Segoe UI;
    font-weight: lighter;
    padding: 10px;
}
.offline {
    background-color: red;
}
.online {
    background-color: green;
}

JavaScript

function isOnline() {
    return navigator.onLine;
}

function checkStatus() {
    var status = document.getElementById("status");
    if (isOnline()) {
        status.className = "online";
        status.innerText = "Online";
    } else {
        status.className = "offline";
        status.innerText = "Offline";
    }
}

(function () {

    window.addEventListener("online", checkStatus);
    window.addEventListener("offline", checkStatus);

    checkStatus();

})();