屏幕大小改变或首次加载计算html根元素 fontsize

/**
* @file 文件的描述
* @author Y50 <yujun.li@partner.midea.com.cn>
* @copyright
* @license Released under the Commercial license.
* @since 1.0.1
* @version 1.0.1 - 2015-9-8
*/
(function (doc, win) {
'use strict';

var devicePixelRatio = win.devicePixelRatio,
viewport = document.createElement('meta');

viewport.name='viewport';
document.getElementsByTagName('head')[0].appendChild(viewport);

//让屏幕按照真实的像素进行渲染 此时1px=1dip 独立像素=实际像素
//viewport.content='initial-scale='+1/devicePixelRatio+', maximum-scale='+1/devicePixelRatio+', minimum-scale='+1/devicePixelRatio+', user-scalable=no';

if (devicePixelRatio === 2) {
viewport.content='initial-scale=0.5, maximum-scale=0.5, minimum-scale=0.5, user-scalable=no';
} else if (devicePixelRatio === 3) {
viewport.content='initial-scale=0.3333333333, maximum-scale=0.3333333333, minimum-scale=0.3333333333, user-scalable=no';
} else {
viewport.content='width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no';
}

var docEl = doc.documentElement,
resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
recalc = function () {
var clientWidth = docEl.clientWidth;
if (!clientWidth) {
return;
}
docEl.style.fontSize = 100 * (clientWidth / 375) + 'px';
};

// Abort if browser does not support addEventListener
if (!doc.addEventListener) return;
//屏幕方向改变或者屏幕大小重新调整后换算 html根元素fontsize 分别对应手机 和 PC
win.addEventListener(resizeEvt, recalc, false);
//加载页面结束后换算文档根元素的fontsize
doc.addEventListener('DOMContentLoaded', recalc, false);
})(document, window);