碰到个很奇怪的问题，用 JS 调用 AS 的函数，和直接用 AS 调用，同一个函数，行为不一样。

public function saveFileToServer(data:ByteArray, filename:String, whenDone:Function):void {
        var values:URLVariables = new URLVariables();
        values.key = "Message";

        var header:URLRequestHeader = new URLRequestHeader("pragma", "no-cache");
        var request:URLRequest = new URLRequest("/save");
        var data = getData();// function to get data to post

        request.contentType = "multipart/form-data; boundary=" + UploadPostHelper.getBoundary();
        request.requestHeaders.push(header);
        request.method = URLRequestMethod.POST;
        request.data = UploadPostHelper.getPostDataMultiFiles(
            {
                data:data
            } );

        var loader:URLLoader = new URLLoader();
        loader.dataFormat = URLLoaderDataFormat.BINARY;
        loader.addEventListener(Event.COMPLETE, whenDone);
        loader.addEventListener(SecurityErrorEvent.SECURITY_ERROR,function(err:ErrorEvent):void
        {
            Scratch.app.logMessage("Failed server request for ");
            ExternalInterface.call("console.log", "SECURITY_ERROR");
        });
        loader.addEventListener(IOErrorEvent.IO_ERROR,function(err:ErrorEvent):void
        {
            Scratch.app.logMessage("Failed server request for ");
            ExternalInterface.call("console.log", "IO_ERROR");
        });
        loader.addEventListener(ProgressEvent.PROGRESS,function(event:ProgressEvent):void
        {
            ExternalInterface.call("console.log", "PROGRESS");
        });
        try {
            ExternalInterface.call("console.log", "Before load");  //正常输出
            loader.load(request);    // 用 JS 调用时，没有效果，没有请求出现。
            ExternalInterface.call("console.log", "After load");   //正常输出
        }
        catch (error:ArgumentError) {
            trace("An ArgumentError has occurred."); // no error caught.
        }
        catch (error:SecurityError) {
            trace("A SecurityError has occurred.");
        }catch (error:*){
            trace("other errors");
        }
    }