几行js代码实现自适应

(function (doc, win, undefined) {      var docEl = doc.documentElement,       resizeEvt = 'orientationchange' in win? 'orientationchange' : 'resize',       recalc = function () {        var clientWidth = docEl.clientWidth;        if (clientWidth === undefined) return;        docEl.style.fontSize = 20 * (clientWidth / 320) + 'px';       };      if (doc.addEventListener === undefined) return;      win.addEventListener(resizeEvt, recalc, false);      doc.addEventListener('DOMContentLoaded', recalc, false)     })(document, window);