Uncaught TypeError: Cannot read property 'style' of undefined

? ? at promise.html:60

????function?promiseAnimate(ball,?distance)?{
????????return?new?Promise(function(resolve,?reject)?{
????????????function?_animate(ball,?distance,?cb)?{
????????????????setTimeout(function()?{
????????????????????var?marginLeft?=?parseInt(?ball.style.marginLeft?,?10)
????????????????????if?(marginLeft?===?distance)?{
????????????????????????resolve()
????????????????????}?else?{
????????????????????????if?(marginLeft?<?distance)?{
????????????????????????????marginLeft++
????????????????????????}?else?{
????????????????????????????marginLeft--
????????????????????????}
????????????????????????ball.style.marginLeft?=?marginLeft?+?'px'
????????????????????????_animate()
????????????????????}
????????????????},?13)
????????????}
????????????_animate()
????????})
????}