ES6 implementation of a CSS supports polyfill

cssSupports.js

/**
 * Read up on the API here https://developer.mozilla.org/en-US/docs/Web/API/CSS/supports
 */

if (!window.CSS) {
  window.CSS = {};
}

if(!RegExp.escape) {
  RegExp.escape = s => String(s).replace(/[\\^$*+?.()|[\]{}]/g, '\\$&');
}

if (!window.CSS.supports) {
  const _hyphenPattern = /-(.)/g;
  const camelize = s => s.replace(_hyphenPattern, 
    (_, character) => character.toUpperCase());
    
  const div = document.createElement("div");

  function checkSupport(propName, value) {
    value = value.replace(/^\s/, "");
    div.setAttribute("style", `${propName}: ${value};`);
    return new RegExp(RegExp.escape(value), "i")
      .test(div.style[camelize(propName)]);
  }

  const splitConditionRx = /(\s+or)(?=\W)/;
  const scoped = /(^\s*\(\s*|\s*\)\s*$)/g;
  const filter = c => !!c && !(/\b\s*or\s*\b/i.test(c));
  const isTrue = b => !!b;
  const multiCheckSupport = s => checkSupport(...s.replace(scoped, "").split(":"));

  window.CSS.supports = (...args) => {
    let hasSupport = false;
    document.body.appendChild(div);

    if (args.length === 2) {
      hasSupport = checkSupport(...args);
    } else if (args.length === 1) {
      hasSupport = args[0].split(splitConditionRx)
        .filter(filter)
        .map(multiCheckSupport)
        .some(isTrue);
    }

    div.parentElement.removeChild(t);
    return hasSupport;
  }
}