line smoothing

blur.js

const blur1 = (data) =>
  data.map((d, i) => {
    const previous = i === 0 ? i : i - 1;
    const next = i === data.length - 1 ? i : i + 1;
    const sum = (data[previous] || 0) + d + (data[next] || 0);
    d = sum / 3;
    return d;
  });

const twice = (fn) => (x) => fn(fn(x));
const fourTimes = (fn) => twice(twice(fn));
const sixtyfourTimes = (fn) => fourTimes(fourTimes(fn));

const blur = (x) => sixtyfourTimes(blur1)(x);

export default blur;