According to the documention a marker is optional with an infoWindow, so how is this achieved please? I have tried infowindow.open(map) and infowindow.open(map,
infowindow.open(map)
makes no sense since you need to specify the position where the infowindow should open, also it has a tapered stem which specifies the location where it should point.
According to the documentation of Infowindows- InfoWindows may be attached to either Marker objects (in which case their position is based on the marker's location) or on the map itself at a specified LatLng.
So if you donot want the marker to open the infowindow, use the map click event-
var iwindow= new google.maps.InfoWindow;
google.maps.event.addListener(map,'click',function(event)
{
iwindow.setContent(event.latLng.lat()+","+event.latLng.lng());
iwindow.open(map,this);
iwindow.open(map,this);
});
And to close a InfowWindow- infowindow.setMap(null);
Hope that cleared your doubts.