Patch Style: get the CSS snippet needed to give one element the style of another

patch-style.js

// get the CSS snippet needed to give one element the style of another

var R = require('ramda');
var getPx = (str) => /(\d+)\s*px/g.test(str) ? Number(str.replace(/[^\d]/g, '')) : null;
var px2rem = R.curry((base, str) => str.replace(/(\d+)\s*px/g, (match, px) => Number(px)/base + 'rem'));
var base = getPx(getComputedStyle(document.documentElement).fontSize);
var toRem = px2rem(base);
var patchStyle = (fromEl, toEl, asRem = false) => {
  let [styles, stylesTo] = [fromEl, toEl].map(getComputedStyle);
  let css = R.pipe(
    R.values,
    R.filter(k => styles[k] != stylesTo[k]),
    R.map(k => [k, styles[k]]),
    R.fromPairs,
    R.map(v => asRem ? toRem(v) : v),
    R.toPairs,
    R.map(([k, v]) => `  ${k}: ${v};`),
    R.join('\n') //,
  )(styles);
  return css; //`{\n${css}\n}`;
}
// var btns = Array.from(document.getElementsByTagName('button'));
// patchStyle(btns[11], btns[10]);