(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(){
        //重置方法
        win.clientWidth = docEl.clientWidth;
        if (!win.clientWidth) return;
        // 改变DOM根节点fontSize大小的值;
        // (屏幕宽度/设计图宽度) = 缩放或扩大的比例值;
        docEl.style.fontSize = 37.5 * (win.clientWidth / 750) + 'px';
    }
    if (!doc.addEventListener) return;
    win.addEventListener(resizeEvent, rescale, false);
    doc.addEventListener('DOMContentLoaded', rescale, false);
})(document, window);