get length of verticies of mask in AE
// based on knowledge by redefinery http://www.redefinery.com/ae/fundamentals/masks/
// and the AECS6 scripting guide also written by redefinery
var layer = app.project.activeItem.selectedLayers[0];
var masksGroup = layer("Masks");
if (masksGroup != null){
var my_maskShape = layer.mask(1).property("ADBE Mask Shape").value;
alert (my_maskShape.vertices.length);
}