How to find user device is GPS on or off in javascript? This code is not working.

<pre>// Function to get location
    function getLocation() {
        navigator.geolocation.getCurrentPosition(function (pos) {
            var lat = pos.coords.latitude;
            var lng = pos.coords.longitude;
            if (lat == null) {
                navigator.notification.alert("GPS not activated!", null, "GPS", "Ok");
            }
            else {
                navigator.notification.alert("Latitude: " + lat + " , Longitude: " + lng, null, "GPS", "Ok");
            }
        });
    }</pre>