Local variables are one of the things CoffeeScript doesn't compile to
modern JavaScript automatically: it uses `var` instead of `const` or
`let`.
Besides, using `$this = $(this)` is usually done to reference the
current object in another function where the current object is a
different one. Here we were using it with no clear purpose.
The `initialize` functions don't need to return anything, since their
returned value is never used.
Returning false is a common practice in jQuery to stop an event, but in
plain JavaScript methods it doesn't have any side effects.
According to the HTML specification:
> The default value is the minimum plus half the difference between the
> minimum and the maximum, unless the maximum is less than the minimum,
> in which case the default value is the minimum.
So for new progress bars, we had a numeric value of `nil` and a range
value of `50`, meaning the input fields weren't in sync.
Manually triggering the event on the progress, while not an ideal
solution (ideally we would be able to define `0` as default), sets the
value of the numeric field.
