The Javascript is only for demonstrating the functionality. It does not effect the styling in anyway, this is the job of the CSS.
It is also worth mentioning that in any application which would use a progress bar, it would require JS to calculate progress, or update the DOM to display it.
It is also worth mentioning that in any application which would use a progress bar, it would require JS to calculate progress, or update the DOM to display it.
As far as being a pure CSS progress bar, it is.