AngularJS: tracking status of each file being uploaded simultaneously

The index you pass to the event handlers refer to the indices in the original array. After every successful call to splice, the array changes and indices are no longer pointing to the same thing.

$scope.files = ['a.jpg', 'b.jpg', 'c.jpg'];
// $scope.files[1] = 'b.jpg'

$scope.files.splice(1,1);
// $scope.files = ['a.jpg', 'c.jpg']
// $scope.files[1] = 'c.jpg'