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);