Bezier basis function.

bezierBasisFunc.js

function splinePt(points, i, n, t){
  let pt1, pt2;
  if(n == 1){
    pt1 = points[i];
    pt2 = points[i+1];
  }else{
    pt1 = splinePt(points, i, n-1, t);
    pt2 = splinePt(points, i+1, n-1, t);
  }
  let npt = p5.Vector.add(p5.Vector.mult(pt1, (1.0-t)), p5.Vector.mult(pt2, t));
  return npt;
}