手机淘宝用JS来动态写meta标签（1像素边框处理方法）

var metaEl = doc.createElement('meta');
var scale = isRetina ? 0.5:1;
metaEl.setAttribute('name', 'viewport');
metaEl.setAttribute('content', 'initial-scale=' + scale + ', maximum-scale=' + scale + ', minimum-scale=' + scale + ', user-scalable=no');
if (docEl.firstElementChild) {
    document.documentElement.firstElementChild.appendChild(metaEl);
} else {
    var wrap = doc.createElement('div');
    wrap.appendChild(metaEl);
    documen.write(wrap.innerHTML);
}