IE8-模擬script onerror

利用VBScript 檢測，有反作用，慎用！

    var loadScript = function () {
        var DOC = document,
            HEAD = document.getElementsByTagName('head')[0];
        // 往head注入一個script
        var injectScript = function(src, beforeInject){
            var script = document.createElement('script');
            beforeInject.call(script);
            script.src = src;
            script.async = true;
            HEAD.insertBefore(script, HEAD.firstChild);
            return script;
        };
        // 銷燬script標籤
        var destoryScript = function(script){
            script.onerror = script.onreadystatechange = script.onload = null;
            if (script.parentNode) {
                script.parentNode.removeChild(script)
            }
            script = null;
        };
        return function(src, success, failure){
            var dfd = $.Deferred();
            if (DOC.dispatchEvent)
                // 對於w3c標準瀏覽器，採用onerror和onload判斷腳本加載狀況
                injectScript(src, function(){
                    var script = this;
                    script.onload = function(_, isAbort){
                        console.log(isAbort);
                        destoryScript(script);
                      //  dfd.resolve();
                    };
                    script.onerror = function(_, isAbort){
                        destoryScript(script);
                     //   dfd.reject();
                    };
                });
            else
                // 對於噁心的IE8-，咱們經過一個vbscript元素，來檢測腳本是否加載成功
                injectScript(src, function(){
                    var vbtest = this, flag = 0;
                    vbtest.language = 'vbscript';
                    var errorHandler = function(){
                        // 錯誤時，判斷腳本是否正在解釋，是則標誌加載成功
                        if (vbtest.readyState == 'interactive') {
                            flag = 1;
                        }
                        return false;
                    };
                    window.attachEvent('onerror', errorHandler);
                    vbtest.onreadystatechange = function(_, isAbort){
                        if (/loaded|complete/.test(this.readyState)) {
                            // 標誌位，當加載成功，置1；
                            if (flag == 1)
                                injectScript(src, function(){
                                    var script = this;
                                    script.onreadystatechange = function(){
                                        if (/loaded|complete/.test(this.readyState)) {
                                            destoryScript(script);
                                           // dfd.resolve();
                                        }
                                    };
                                });
                            else {
                              //  dfd.reject();
                            }
                            // 爲window綁定一個錯誤，當js被誤加載成vb的時候，會發生錯誤，來判斷是否加載成功
                            window.detachEvent('onerror', errorHandler);
                            destoryScript(vbtest);
                        }
                    };
                });
            // 綁定成功失敗
          //  if (typeof success == 'function') dfd.done(success);
         //   if (typeof failure == 'function') dfd.fail(failure);
          //  return dfd;
        };
    }();