dwr文件上传在chrome下的问题及解决方法

今天发现dwr的文件上传在chrome下使用不了，无法只得跟踪源码，错误在源码的方法：

   beginLoader:function(batch, idname) {
        batch.iframe = batch.document.getElementById(idname);
        batch.iframe.batch = batch;
        batch.mode = batch.isPoll ? dwr.engine._ModeHtmlPoll : dwr.engine._ModeHtmlCall;
        if (batch.isPoll) dwr.engine._outstandingIFrames.push(batch.iframe);
        var request = dwr.engine.batch.constructRequest(batch, batch.httpMethod);
        if (batch.httpMethod == "GET") {
          batch.iframe.setAttribute("src", request.url);
        }
        else {
          // TODO: On firefox we can now get the values of file fields, maybe we should use this
          // See http://soakedandsoaped.com/articles/read/firefox-3-native-ajax-file-upload
          // setting enctype via the DOM does not work in IE, create the form using innerHTML instead
          var formHtml = "<form id='dwr-form' action='" + request.url + "' target='" + idname + "' style='display:none;' method='" + batch.httpMethod + "'";
          if (batch.encType) formHtml += " enctype='" + batch.encType + "'";
          formHtml += "></form>";
          var div = batch.document.createElement("div");
          div.innerHTML = formHtml;
          batch.form = div.firstChild;
          for (var prop in batch.map) {
            var value = batch.map[prop];
            if (typeof value != "function") {
              if (value.tagName && value.tagName.toLowerCase() == "input" && value.type && value.type.toLowerCase() == "file") {
                // Since we can not set the value of a file object, we must post the actual file object
                // that the user clicked browse on. We will put a clone in it's place.
                var clone = value.cloneNode(true);
                value.removeAttribute("id", prop);
                value.setAttribute("name", prop);
                value.parentNode.insertBefore(clone, value);
                value.parentNode.removeChild(value);
                batch.form.appendChild(value);
              } else {
                var formInput = batch.document.createElement("input");
                formInput.setAttribute("type", "hidden");
                formInput.setAttribute("name", prop);
                formInput.setAttribute("value", value);
                batch.form.appendChild(formInput);
              }
            }
          }
          batch.document.body.appendChild(batch.form);
          batch.form.submit();
        }
      },

 

注：红色部分就是出错的地方，这个batch取出来是个null值，导致无法进行下去

继续跟踪，确定错误的源头就是下面这个方法：

  send:function(batch) {
        if (batch.fileUpload) {
          batch.httpMethod = "POST";
          batch.encType = "multipart/form-data";
        }
        var idname = dwr.engine.transport.iframe.getId(batch);
        batch.div = document.createElement("div");
        // Add the div to the document first, otherwise IE 6 will ignore onload handler.
        document.body.appendChild(batch.div);
        batch.div.innerHTML = "<iframe src='javascript:void(0)' frameborder='0' style='width:0px;height:0px;border:0;' id='" + idname + "' name='" + idname + "' onload='dwr.engine.transport.iframe.loadingComplete(" + batch.map.batchId + ");'></iframe>";
        batch.document = document;
        dwr.engine.transport.iframe.beginLoader(batch, idname);
      },

注：红色部分就是造成appendChild方法失效的源头，造成这种情况的原因在于iframe的onload事件，而造成这个情况的是调用方法中的dwr.engine.batch.validate(batch)方法造成的，
为什么这个方法会造成chrome浏览器没有吧div节点加入到dom树中，原因我不是很清楚

  loadingComplete:function(batchId) {
        var batch = dwr.engine._batches[batchId];
        if (batch) dwr.engine.batch.validate(batch);
      },
那么解决的方法是，重写这个方法，加入对chrome浏览器的判断，解决方法：

var isChrome = (/\bchrome\b/).test(navigator.userAgent.toLowerCase());
dwr.engine.transport.iframe.loadingComplete = function(batchId) {
        var batch = dwr.engine._batches[batchId];
        if(!isChrome)
        if (batch) dwr.engine.batch.validate(batch);
      };

如果各位有更好的解决方法，或者有更好的见解，多指教