Detect if a set of points in an array that are the vertices of a complex polygon were defined in a clockwise or counterclockwise order?

Question

EDIT: I updated the program with the answer and it works great!

I am making a program (feel free to try it out) that lets users draw polygons which it then triangulates.

Answer 1

This a function function that specialized for OpenLayers. As You Can See The Condition Of Clockwise Polygon Is area<0 This Reference Confirm It.

function IsClockwise(feature)
{
if(feature.geometry==null)return -1;
var vertices=feature.geometry.getVertices();
var area=0;
for (var i = 0; i < (vertices.length); i++) 
    {
    j = (i + 1) % vertices.length;
    area += vertices[i].x * vertices[j].y;
    area -= vertices[j].x * vertices[i].y;
    // console.log(area);
    }
return (area < 0);
}