在ie中xdomainrequest的问题

Question

我使用以下代码在Internet Explorer中执行跨域操作。

if (window.XDomainRequest) { // Check whether the browser supports XDR. 
    xdr = new XDomainRequest(); // Create a new XDR object.
    if (xdr) {
        // There is an error and the request cannot be completed. 
        // For example, the network is not available.
        xdr.onerror = alert_error;

        // This event is raised when the request reaches its timeout. 
        xdr.ontimeout = alert_timeout;
        obj['username'] = username;
        obj['password'] = password;

        // When the object starts returning data, the onprogress event 
        // is raised and the data can be retrieved by using responseText.
        xdr.onprogress = alert_progress;

        // When the object is complete, the onload event is raised and 
        // the responseText ensures the data is available. 
        xdr.onload = alert_loaded;

        xdr.timeout = 5000;

        // The URL is preset in the text area. This is passed in the 
        // open call with a get request.
        xdr.open("post", action);
    }

    // The request is then sent to the server.  
    xdr.send(JSON.stringify(obj));
}

数据保存在JSON对象中，该对象在作为XDomainRequest的一部分发送之前进行了字符串化。

但不知怎的JSON.stringify(obj)正在发送空值。