Variable seems to not get set on mobile devices

I'm reading an image file and rescaling it to send it to a server. In order to properly rescale it I need to change the orientation, since some pictures are taken with a mobile device camera. In order to do this rotation I did the following using the exif.js library:

EXIF.getData(img, function() {    
    alert(this.exifdata.Orientation);
    orientation = this.exifdata.Orientation;
    alert(orientation);
}

If this.exif.data.Orientation was, for example 6, the following output would be desierd: "6", "6".

This works when a file is uploaded via my computer. However, when uploaded from a mobile device camera, the output is "6" and then "0", no matter what value orientation had before.

Why does this happen?

Note: I'm only running on one thread. So the variable could not have been set externally during execution of these lines.

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