Three kinds of cubic spline calculation in CoffeeScript: natural, clamped and monotonic.
Note: there may be glitches in the monotonic calculations that cause non-monotonicity on rare occasions (best I can tell, these are in the original sources, not my translation).
Demo, discussion, and compiled JS: http://blog.mackerron.com/2011/01/01/javascript-cubic-splines/
Licence: MIT
Original code by George MacKerron https://github.com/jawj
Typescript declarations by Claudio Schilling https://github.com/rbfowler9lfc
As of 2021 Coffeescript is basically dead on the water, so running npm install will compile the source into a CommonJS module, and a Typescript declaration file is also available.
npm install https://github.com/rbfowler9lfc/cubicsplines.git
import { MonotonicCubicSpline, CubicSpline } from "cubicsplines";
const xs = [0, 1, 2, 3, 4];
const ys = [9, 3, 6, 2, 4];
const cubic = new CubicSpline(xs, ys);
const monotonic = new MonotonicCubicSpline(xs, ys);
// Get Y at arbitrary X
console.log(cubic.interpolate(1.4)); // Outputs 4.075319916724497
console.log(monotonic.interpolate(1.4)); // Outputs 3.888