function loadJs(jsFile){
    if (!jsFile) return; var oHead = document.getElementsByTagName('HEAD')[0];
    alert(oHead);
    var oScript = document.createElement('script');
    oScript.type = "text/javascript"; oScript.src = jsFile; oHead.appendChild(oScript);
}
loadJs("http://xxx.com/inc/js/jquery-1.7.1.min.js/");  //加载jquery.

//加载后 后面的代码失效！
$(function(){
alert("fdsfds");
})