doc.createElem('meta'); Uncaught ReferenceError: doc is not defined

<script>
    //手机淘宝显示
    var metaEl = doc.createElem('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.createElem('div');
        wrap.appendChild(metaEl);
        document.write(wrap.innerHTML);
    }
</script>