移动端动态计算根元素的字体大小

(function (doc, win) {
	var docEl = doc.documentElement, //文档根标签
	    resizeEvent = 'orientationchange' in window ? 'orientationchang' : 'resize'; //viewport变化事件源
	var rescale = function () {
	    win.clientWidth = docEl.clientWidth;
	    if (!win.clientWidth) return;
	    // (屏幕宽度/设计图宽度) = 缩放或扩大的比例值;
	    docEl.style.fontSize = 36 * (win.clientWidth / 375) + 'px';
	}
	if (!doc.addEventListener) return;
	win.addEventListener(resizeEvent, rescale, false);
	doc.addEventListener('DOMContentLoaded', rescale, false);
})(document, window);