js自动换算成rem

(function (doc, win, pwidth, prem) {
        var docEl = doc.documentElement,
                resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
                recalc = function () {
                  var clientWidth = docEl.clientWidth;
                  if (!clientWidth) return;
                  docEl.style.fontSize = clientWidth / pwidth * prem + 'px';
                };
        if (!doc.addEventListener) return;
        win.addEventListener(resizeEvt, recalc, false);
        doc.addEventListener('DOMContentLoaded', recalc, false);
      })(document, window, 1920, 100); //设计图大小和需要换算的单位