移动的rem自适应

(function (doc, win) {
	var docEl = doc.documentElement, //html
		resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize', //事件名称
		recalc = function () {
			var clientWidth = docEl.clientWidth;
			if (!clientWidth) return;
			if (clientWidth >= 640) {
				docEl.style.fontSize = '100px';
            }
			else {
				docEl.style.fontSize = 100 * (clientWidth / 640) + 'px';
			}
		};

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