Edit in JSFiddle

var map;

function initialize() 
{
  var mapOptions = 
  {
    zoom: 6,
    mapTypeId: google.maps.MapTypeId.ROADMAP
  };
    
  map = new google.maps.Map(document.getElementById('map-canvas'),
      mapOptions);

  // Try HTML5 geolocation
  if(navigator.geolocation) 
  {
    navigator.geolocation.getCurrentPosition(function(position) 
    {
      var pos = new google.maps.LatLng(position.coords.latitude,
                                       position.coords.longitude);

      var infowindow = new google.maps.InfoWindow(
      {
        map: map,
        position: pos,
        content: 'Location found using HTML5.'
      });

      map.setCenter(pos);
    }, function() 
    {
      handleNoGeolocation(true);
    });
  } else {
    // Browser doesn't support Geolocation
    handleNoGeolocation(false);
  }
}

function handleNoGeolocation(errorFlag) 
{
  if (errorFlag) {
    var content = 'Error: The Geolocation service failed.';
  } else {
    var content = 'Error: Your browser doesn\'t support geolocation.';
  }

  var options = {
    map: map,
    position: new google.maps.LatLng(60, 105),
    content: content
  };

  var infowindow = new google.maps.InfoWindow(options);
  map.setCenter(options.position);
}
initialize();
//google.maps.event.addDomListener(window, 'load', initialize);

<div id="map-canvas">loading map</div>

  html { height: 100% }
  body { height: 100%; margin: 0; padding: 0 }
#map-canvas{
    width:100%;
    height:100%;
}