point-in-polygon.js

var pointInPolygon = function(point, polygon) {
	var x = point[0], y = point[1];

	var inside = false;
	for (var i = 0, j = polygon.length - 1; i < polygon.length; j = i++) {
		var xi = polygon[i][0], yi = polygon[i][1];
		var xj = polygon[j][0], yj = polygon[j][1];

		var intersect = ((yi > y) != (yj > y)) && (x < (xj - xi) * (y - yi) / (yj - yi) + xi);

		if (intersect) {
			inside = !inside;
		}
	}

	return inside;
};