Close all infowindows in Google Maps API v3 [duplicate]

infowindow is local variable and window is not available at time of close()

var latlng = new google.maps.LatLng(-34.397, 150.644);
var infowindow = null;

...

google.maps.event.addListener(marker, 'click', function() {
    if (infowindow) {
        infowindow.close();
    }
    infowindow = new google.maps.InfoWindow();
    ...
});
...