Why are there no properties in the Backbone obj?

I worked on some drag and drop functions and added events through the standard Backbone method:

events: { 
 'dragenter': 'dragEnter',
 'dragend': 'dragEnd'
 ....,
 .....
}

In my function, I noticed that the object eventthat is passed into it does not contain some of the properties described in the html5 specification.

In particular, dataTransferobj is missing .

I created a demo to demonstrate my problem . Just drag and drop a file or something in it to see it in the logs.

My question is: why is this happening? I looked through the documentation and didn't seem to find it.