it looks like, when bootstrap storing any into jQuery.fn.data(), they add 'bs.' as prefix of the data name.

https://github.com/phariel/ef-bootstrap/blob/8f8927ca8baffbad081eef816f59e92674dae0e7/js/popover.js#L98

also, I would prefer to pack all properties into one single object, rather than storing them separately into data(), something like:

  var data = $this.data('bs.stepper)

  if (!data) {
    data = {
      max: xxx,
      min: xxx,
      step: 1,
      lastValue: 0    
    }
  $this.data('bs.stepper', data)