简单的动态加载 js 和 css

function importJs(filename)
{
    var ref = document.createElement("script");
    ref.setAttribute("type", "text/javascript");
    ref.setAttribute("src", filename);

    if (typeof ref != undefined)
         document.getElementsByTagName("head")[0].appendChild(ref);
}
function importCss(filename)
{
    var ref=document.createElement("link");
    ref.setAttribute("rel", "stylesheet");
    ref.setAttribute("type", "text/css");
    ref.setAttribute("href", filename);

    if (typeof ref != undefined)
         document.getElementsByTagName("head")[0].appendChild(ref);
}