Extjs 4上传成功功能没有反应

我有一个带有工具栏的网格，并且在该工具栏上添加了上传选项，因此上传是正确的并且它可以工作，但是在文件上传到服务器后，成功函数没有反应。

这里是我的上传代码:

upload: function () {
        Ext.create('Ext.window.Window', {
            title: 'Upload',
            width: 300,
            layout: 'fit',
            draggable: false,
            resizable: false,
            modal: true,
            bodyPadding: 5,

            items: [{
                xtype: 'form',
                bodyPadding: 10,
                frame: true,
                items: [{
                    xtype:'filefield',
                    name:'file',
                    fieldLabel: 'File',
                    buttonText: 'Select File',
                    labelWidth: 30,
                    anchor: '100%'
                }, {
                    xtype: 'button',
                    text: 'Upload',
                    handler: function(){                        
                         var form = this.up('form').getForm();
                         if(form.isValid()){
                             form.submit({  
                                 method: 'POST',     
                                 url: 'http://localhost:3000/upload',
                                 success: function (form, action) {
                                     Ext.Msg.alert('Success', 'Your File has been uploaded.');
                                     console.log(action);
                                 },
                                 failure : function (form,action) {
                                     Ext.Msg.alert('Error', 'Failed to upload file.');
                                 }
                             })
                         }
                    }
                }] 
            }],
        }).show();
    },  
});

和服务器响应:

app.post('/upload', function(req, res) {
    res.header('Access-Control-Allow-Origin', '*');
    res.header('Content-Type','application/json; charset=UTF8');
    var tmp_path = req.files.file.path;
    var newPath = __dirname + '/files/' + req.files.file.name;
    fs.rename(tmp_path, newPath, function (err){
        if (err) throw err;
    });

    var path = newPath;
    var name = req.files.file.name; 
    connection.query('SELECT name FROM audio WHERE name = ?', [name] , function(err,result) {
        if (result[0]) {
            console.log('File already exist');
            res.status(400).send(JSON.stringify());
        } else {
            connection.query('INSERT INTO audio (name, path) VALUES (?,?)', [name,path], function (err,result) {
                if (err) throw err;
                var test = {
                    success: true
                };
                res.send({success:true});
                console.log('success');
            });

        }
    });

});

如果需要，我可以提供更多的代码，提前感谢