移动端rem布局

!function (window) {
/* 设计图文档宽度 */
var docWidth = 750;

var doc = window.document,
docEl = doc.documentElement,
resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize';

var recalc = (function refreshRem () {
var clientWidth = docEl.getBoundingClientRect().width;

/* 8.55：小于320px不再缩小，11.2：大于420px不再放大 */
docEl.style.fontSize = Math.max(Math.min(20 * (clientWidth / docWidth), 11.2), 8.55) * 5 + 'px';

return refreshRem;
})();

/* 添加倍屏标识，安卓为1 */
docEl.setAttribute('data-dpr', window.navigator.appVersion.match(/iphone/gi) ? window.devicePixelRatio : 1);

if (/iP(hone|od|ad)/.test(window.navigator.userAgent)) {
/* 添加IOS标识 */
doc.documentElement.classList.add('ios');
/* IOS8以上给html添加hairline样式，以便特殊处理 */
if (parseInt(window.navigator.appVersion.match(/OS (\d+)_(\d+)_?(\d+)?/)[1], 10) >= 8)
doc.documentElement.classList.add('hairline');
}

if (!doc.addEventListener) return;
window.addEventListener(resizeEvt, recalc, false);
doc.addEventListener('DOMContentLoaded', recalc, false);
}(window);