px换算rem

记录一些简易版本px换算rem的封装方法；根据UI设计稿来换算如：pc端：1920；h5端：750

(function (doc, win) {
  let fn = function fn() {
    let docEl = doc.documentElement;
    let clientWidth = docEl.clientWidth;
    if (!clientWidth) return;
    docEl.style.fontSize = 100 * (clientWidth / 1920) + 'px';
  };
  fn();

  if (!doc.addEventListener) return;
  win.addEventListener('resize', fn);
  doc.addEventListener('DOMContentLoaded', fn);
  window.CALCULATE_SIZE = function (value) {
    return Math.ceil((parseFloat(value) / 1920) * window.innerWidth);
  };
})(document, window);