异步载入js文件

import.js

function importJs(jsurl, fCallback, fError){
        if (typeof(fCallback) != "function") fCallback = new Function();
        if (typeof(fError) != "function") fError = new Function();

        var oScriptEl, oTimeoutHDL, oHead;
         oScriptEl = document.createElement("script");
         oScriptEl.type = "text/javascript";
         oScriptEl.language = "javascript";
         oScriptEl.src = jsurl;
         oScriptEl.onreadystatechange = doCallback;
         oScriptEl.onload = function() {
                this.readyState = "complete";
                 doCallback();
             };

         oTimeoutHDL = window.setTimeout(doError, 20000);
         document.getElementsByTagName("head")[0].appendChild(oScriptEl);

        function doCallback(){
            if (oScriptEl.readyState == "complete" || oScriptEl.readyState == "loaded") {
                 oScriptEl.onload = oScriptEl.onreadystatechange = new Function();
                 fCallback();
                 window.clearTimeout(oTimeoutHDL);
                 oScriptEl.parentNode.removeChild(oScriptEl);
             }
         };

        function doError(){
             oScriptEl.parentNode.removeChild(oScriptEl);
         };
    };