// points [[x1, y1], [x2, y2], ...]
// edges [[start1, end1], [start2, end2]...] starts and ends are indices of points
var dcel = new dcel(points, edges);

// return internal faces
var faces = dcel.internalFaces();

// get holes
faces[0].holes

// get area
faces[0].area

// get area except holes
faces[0].areaExceptHoles

// return external faces
dcel.externalFaces();

// edges modify
dcel.addEdge(x1, y1, x2, y2);
dcel.removeEdge(x1, y1, x2, y2);
dcel.splitEdge(x1, y1, x2, y2, splitX, splitY);