Google Map Marker not being replaced - google-maps-api-3

Question

please excuse a noob at this. When a user clicks on a map, it should place a marker and open an info window - as per this example: http://www.geocodezip.com/v3_example_click2add_infowindow.html
The code below almost works correctly, except that the mark is not replaced - a new one is added. Any ideas really, really gratefully received. Thank you.
<script>
var map = null;
var markersArray = [];
function initialize() {
var latlng = new google.maps.LatLng(0.0000, 0.0000);
var settings = {
zoom: 2,
mapTypeControl:true,
center: latlng,
panControl:true,
zoomControl:true,
streetViewControl:false,
overviewMapControl:false,
rotateControl:true,
scaleControl: true,
navigationControl: true,
navigationControlOptions: {
style: google.maps.NavigationControlStyle.DEFAULT
},
mapTypeId: google.maps.MapTypeId.ROADMAP,
backgroundColor: 'white'
};
map = new google.maps.Map(document.getElementById('map'), settings);
function placeMarker(location) {
var marker , i ;
if ( marker ) {
marker.setPosition(location);
} else {
marker = new google.maps.Marker({
position: location,
icon:'http://www.desperatesailors.com/templates/Live/media/mapicons/info.png',
map: map
});
var infowindow = new google.maps.InfoWindow({
content: 'Latitude: ' + location.lat() +
'<br>Longitude: ' + location.lng() +
'<br>Only the first four decimal places needed'
});
infowindow.open(map,marker);
}
}
google.maps.event.addListener(map, 'click', function(event) {
placeMarker(event.latLng);
});
}
window.onload = initialize;
</script>

Answer 1

This is a scope issue. You are always delcaring marker in the placeMarker function so if( marker ) will always be false. Move the variable declaration out of that function:
<script>
var marker;
var map = null;
var markersArray = [];
function initialize() {
var latlng = new google.maps.LatLng(0.0000, 0.0000);
var settings = {
zoom: 2,
mapTypeControl:true,
center: latlng,
panControl:true,
zoomControl:true,
streetViewControl:false,
overviewMapControl:false,
rotateControl:true,
scaleControl: true,
navigationControl: true,
navigationControlOptions: {
style: google.maps.NavigationControlStyle.DEFAULT
},
mapTypeId: google.maps.MapTypeId.ROADMAP,
backgroundColor: 'white'
};
map = new google.maps.Map(document.getElementById('map'), settings);
function placeMarker(location) {
var i ;
if ( marker ) {
marker.setPosition(location);
} else {
marker = new google.maps.Marker({
position: location,
icon:'http://www.desperatesailors.com/templates/Live/media/mapicons/info.png',
map: map
});
var infowindow = new google.maps.InfoWindow({
content: 'Latitude: ' + location.lat() +
'<br>Longitude: ' + location.lng() +
'<br>Only the first four decimal places needed'
});
infowindow.open(map,marker);
}
}
google.maps.event.addListener(map, 'click', function(event) {
placeMarker(event.latLng);
});
}
window.onload = initialize;
</script>

Answer 2

Your placeMarker function creates a new (empty) marker variable in the local scope.
function placeMarker(location) {
var marker , i ;
if ( marker ) {
It will always create a new marker. Change it to:
var marker = null;
function placeMarker(location) {
if ( marker ) {