Mesh Surface Area

var surfaceArea = function(mesh) {
    if (!mesh) {
        return 0.0;
    }
    var ar = 0.0;
    
    var indices = mesh.getIndices();
    var nbFaces = indices.length / 3;
    
    for (let i = 0; i < nbFaces; i++) {
        ar = ar + facetArea(mesh, i);
    }
    return ar;
};

var facetArea = function(mesh, faceId) {
    if(!mesh) {
        return 0.0;
    }
    var indices = mesh.getIndices();
    if(faceId < 0 || faceId > nbFaces) {
        return 0.0;
    }
    var nbFaces = indices.length / 3;
    var positions = mesh.getVerticesData(BABYLON.VertexBuffer.PositionKind);
    var v1x = 0.0;
    var v1y = 0.0;
    var v1z = 0.0;
    var v2x = 0.0;
    var v2y = 0.0;
    var v2z = 0.0;
    var crossx = 0.0;
    var crossy = 0.0;
    var crossz = 0.0;
    var ar = 0.0;
    var i1 = 0;
    var i2 = 0;
    var i3 = 0;

    i1 = indices[faceId * 3];
    i2 = indices[faceId * 3 + 1];
    i3 = indices[faceId * 3 + 2];
    v1x = positions[i1 * 3] - positions[i2 * 3];
    v1y = positions[i1 * 3 + 1] - positions[i2 * 3 + 1];
    v1z = positions[i1 * 3 + 2] - positions[i2 * 3 + 2];
    v2x = positions[i3 * 3] - positions[i2 * 3];
    v2y = positions[i3 * 3 + 1] - positions[i2 * 3 + 1];
    v2z = positions[i3 * 3 + 2] - positions[i2 * 3 + 2];
    crossx = v1y * v2z - v1z * v2y;
    crossy = v1z * v2x - v1x * v2z;
    crossz = v1x * v2y - v1y * v2x; 

    return Math.sqrt(crossx * crossx + crossy * crossy + crossz * crossz) * 0.5;
}