How to determine when loading an xml file is completed?

hi,
I want to load an xml file using javascript in a web page.
And I use firefox 0.9.3 to visit the page.

The code below is load the xml file.
    this.xmlDoc = document.implementation.createDocument("","doc",null);
    this.xmlDoc.load(url);

I want to make sure the xml file is loaded successfully, or to time out at 5 
seconds.
there is no property such as this.xmlDoc.readyState to check.

Is this.xmlDoc.onload a good way to detect the completion of loading?
What if i have to time out the loading after 5 seconds?

Any suggestion?

Thanks,
Roy