Grouping points after cut plane three js with new library

Question

Regarding the discussion in this link, where the object is a THREE.Geometry(), anyone has any idea to implement this code:

function getContours(points, contours, firstRun) {
  //console.log("firstRun:", firstRun);

  let contour = [];

  // find first line for the contour
  let firstPointIndex = 0;
  let secondPointIndex = 0;
  let firstPoint, secondPoint;
  for (let i = 0; i < points.length; i++) {
    if (points[i].checked == true) continue;
    firstPointIndex = i;
    firstPoint = points[firstPointIndex];
    firstPoint.checked = true;
    secondPointIndex = getPairIndex(firstPoint, firstPointIndex, points);
    secondPoint = points[secondPointIndex];
    secondPoint.checked = true;
    contour.push(firstPoint.clone());
    contour.push(secondPoint.clone());
    break;
  }

  contour = getContour(secondPoint, points, contour);
  contours.push(contour);
  let allChecked = 0;
  points.forEach(p => { allChecked += p.checked == true ? 1 : 0; });
  console.log("allChecked: ", allChecked == points.length);
  if (allChecked != points.length) { return getContours(points, contours, false); }
  return contours;
}

  function getContour(currentPoint, points, contour){
  let p1Index = getNearestPointIndex(currentPoint, points);
  let p1 = points[p1Index];
  p1.checked = true;
  let p2Index = getPairIndex(p1, p1Index, points);
  let p2 = points[p2Index]; 
  p2.checked = true;
  let isClosed = p2.equals(contour[0], tolerance);
  if (!isClosed) {
    contour.push(p2.clone());
    return getContour(p2, points, contour);
  } else {
    contour.push(contour[0].clone());
    return contour;
  }
}

function getNearestPointIndex(point, points){
  let index = 0;
  for (let i = 0; i < points.length; i++){
    let p = points[i];
    if (p.checked == false && p.equals(point, tolerance)){ 
      index = i;
      break;
    }
  }
  return index;
}

function getPairIndex(point, pointIndex, points) {
  let index = 0;
  for (let i = 0; i < points.length; i++) {
    let p = points[i];
    if (i != pointIndex && p.checked == false && p.faceIndex == point.faceIndex) {
      index = i;
      break;
    }
  }
  return index;
}

With new three library the object is a THREE.BufferGeometry() that has no face(s) and no checked.

I need to connect the points between themselves (separate arrays) where the plane passes.