响应式页面计算rem代码

(function (doc, win) {
	var docEl     = doc.documentElement,
	    resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
	    recalc    = function () {
		    var clientWidth = docEl.clientWidth;
		    if (clientWidth > 640) {
			    clientWidth = 640;
		    }
		    if (!clientWidth) return;
		    docEl.style.fontSize = 20 * (clientWidth / 320) + 'px';
	    };

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

PS：在写自适应页面时最好在头部加上

<meta name="viewport" content="width=device-width, initial-scale=1.0, minimum-scale=1.0,  maximum-scale=1.0, user-scalable=no"/>