XmlHttpRequest2 progress event and ExtJS 3.3 Ext.Ajax

I'm trying to use XmlHttpRequest Level 2 to create a 开发者_如何学编程file upload page which includes a progress bar, in a fashion similar to a tutorial I found on Matlus.com.

The catch is, the page I'm working on has to be added to an existing ExtJs 3 application.

How can I manipulate the XmlHttpRequest objects which are created by Ext.Ajax, so I can add event listeners for "progress"?

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According to the code, Ext.Ajax.request actually returns a hashmap, not a number like the documentation suggests. You should be able to get the XMLHttpRequest object by referencing Ext.Ajax.request(...).conn and calling addEventListener on that.