This is a Javascript Google Maps v3 extension for the Polygon class to detect whether or not a point resides within it.
Simplest Usage:
var coordinate = new google.maps.LatLng(40, -90);
var polygon = new google.maps.Polygon([], "#000000", 1, 1, "#336699", 0.3);
var isWithinPolygon = polygon.containsLatLng(coordinate);