Polygon centroid - typescript or javascript

get-polygon-centroid.ts

/**
 * https://en.wikipedia.org/wiki/Centroid#Of_a_polygon
 */
public getPolygonCentroid(vertices: number[][]): { lat: number, lon: number } {
    const centroid: { lat: number, lon: number } = { lat: 0, lon: 0 };
    const vertexCount: number = vertices.length;

    let area: number = 0;
    let x0: number = 0; // Current vertex X
    let y0: number = 0; // Current vertex Y
    let x1: number = 0; // Next vertex X
    let y1: number = 0; // Next vertex Y
    let a: number = 0;  // Partial signed area
    let i: number = 0; // Counter

    for (; i < vertexCount - 1; ++i) {
      x0 = vertices[i][0];
      y0 = vertices[i][1];
      x1 = vertices[i + 1][0];
      y1 = vertices[i + 1][1];

      a = x0 * y1 - x1 * y0;

      area += a;

      centroid.lon += (x0 + x1) * a;
      centroid.lat += (y0 + y1) * a;
    }

    // Do last vertex separately to avoid performing an expensive
    // modulus operation in each iteration.
    x0 = vertices[i][0];
    y0 = vertices[i][1];
    x1 = vertices[0][0];
    y1 = vertices[0][1];

    a = x0 * y1 - x1 * y0;

    area += a;
    centroid.lon += (x0 + x1) * a;
    centroid.lat += (y0 + y1) * a;
    area *= 0.5;

    centroid.lon /= (6 * area);
    centroid.lat /= (6 * area);

    return centroid;
  }