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()
        })
    }