docs/bundle.js
function slope3(that, x2, y2) {
  var h0 = that._x1 - that._x0,
      h1 = x2 - that._x1,
      s0 = (that._y1 - that._y0) / (h0 || h1 < 0 && -0),
      s1 = (y2 - that._y1) / (h1 || h0 < 0 && -0),
      p = (s0 * h1 + s1 * h0) / (h0 + h1);
  return (sign(s0) + sign(s1)) * Math.min(Math.abs(s0), Math.abs(s1), 0.5 * Math.abs(p)) || 0;
}
function slope3(that, x2, y2) {
  var h0 = that._x1 - that._x0,
      h1 = x2 - that._x1,
      s0 = (that._y1 - that._y0) / (h0 || h1 < 0 && -0),
      s1 = (y2 - that._y1) / (h1 || h0 < 0 && -0),
      p = (s0 * h1 + s1 * h0) / (h0 + h1);
  return (sign(s0) + sign(s1)) * Math.min(Math.abs(s0), Math.abs(s1), 0.5 * Math.abs(p)) || 0;
}
Calculate the slopes of the tangents (Hermite-type interpolation) based on the following paper: Steffen, M. 1990. A Simple Method for Monotonic Interpolation in One Dimension. Astronomy and Astrophysics, Vol. 239, NO. NOV(II), P. 443, 1990.