My code is not working

 <script>
var x = document.getElementById("demo");
function getLocation() {
 if (navigator.geolocation) {
    navigator.geolocation.getCurrentPosition(showPosition);
  } else {
    x.innerHTML = "Geolocation is not supported by this browser.";
  }
}

function showPosition(position) {
  x.innerHTML = "Latitude: " + position.coords.latitude + 
 "<br>Longitude: " + position.coords.longitude; 
}
</script> 

In x.innerHTML = "Latitude:

How I do change the value?