var loadScript = function (url, callback) {
    var script = document.createElement("script");
    script.src = url;

    document.getElementsByTagName("head")[0].appendChild(script);

    if (script.addEventListener) {

        // for w3c
        script.onload = function () {
            script.onload = null;
            script.parentNode.removeChild(script);

            callback && callback();
        };
    } else if (script.readyState) {
    
        // for ie
        script.onreadystatechange = function () {

            if (script.readyState === "loaded" || script.readyState === "complete") {

                script.onreadystatechange = null;
                script.parentNode.removeChild(script);

                callback && callback();
            }
        };
    } else {

        // for lower brower
        script.parentNode.removeChild(script);
        callback && callback();
    }
};

var loadStyle = function (cssText) {
    var style = document.createElement("style");
    style.type = "text/css";
    style.rel = "styleSheet";

    try {
        style.appendChild(document.createTextNode(cssText));
    } catch (ex) {
        // for ie
        style.styleSheet.cssText = cssText;
    }

    document.getElementsByTagName("head")[0].appendChild(style);
};

loadStyle("body{background-color:#aaa;}");