Ext4 controller中Ajax的scope会污染this指针

login: function (loginId, password, callback) {
        Ext.Ajax.request({
            url: UserService + '/Login',
            success: this.onLoginSuccess,
            method: 'POST',
            scope: callback, // 注意，这里会改变其他方法中的this指针
            params: {
                loginId: loginId,
                password: password
            }
        });
},
        
onLoginSuccess: function(){
 // 这里的this指向的是上面的callback
}