function polygonArea(points)
{
var i, j;
var area = 0;
for (i = 0; i < points.length; i++)
{
j = (i + 1) % points.length;
area += points[i].x * points[j].y;
area -= points[i].y * points[j].x;
}
area /= 2;
return Math.abs(area);
}原文：http://blog.csdn.net/jcx5083761/article/details/43935947