JScript Runtime Error

var QScroller = new Class({
    options: {
        slides: 'qslide',
        direction: 'h',
        duration: 3000,
        auto: false,
        delay: 1000,
        transition: Fx.Transitions.linear
    },
    initialize: function(wrapper, options) {
        this.setOptions(options);
        this.wrapper = $(wrapper);
        this.wrapper.setStyles({
            position: 'relative',
            overflow: 'hidden'
        });
        this.wrapper.addEvent('mouseenter', this.fireEvent.pass('onMouseEnter', this));
        this.wrapper.addEvent('mouseleave', this.fireEvent.pass('onMouseLeave', this));

        this.slideOut = new Element('div').setStyles({
            position: 'absolute',
            overflow: 'hidden',
            top: 0,
            left: 0,
            width: this.wrapper.getStyle('width'),
            height: this.wrapper.getStyle('height')
        }).injectInside(this.wrapper);

        this.slideIn = this.slideOut.clone();
        this.slideIn.injectInside(this.wrapper);

        this.slides = $$('.' + this.options.slides);

        if ($defined(this.options.buttons)) {
            if ($defined(this.options.buttons.next)) {
                $(this.options.buttons.next).addEvent('click', this.next.bind(this));
            }
            if ($defined(this.options.buttons.prev)) {
                $(this.options.buttons.prev).addEvent('click', this.prev.bind(this));
            }
            if ($defined(this.options.buttons.play)) {
                $(this.options.buttons.play).addEvent('click', this.play.bind(this));
            }
            if ($defined(this.options.buttons.stop)) {
                $(this.options.buttons.stop).addEvent('click', this.stop.bind(this));
            }
        }
        this.auto = this.options.auto;
        this.idxSlide = 0;
        this.step = 0;
        this.isFirst = true;
    },
    load: function() {
        if (!this.isFirst) {
            this.idxSlide += this.step;
            if (this.idxSlide > this.slides.length - 1) {
                this.idxSlide = 0;
            } else if (this.idxSlide < 0) {
                this.idxSlide = this.slides.length - 1;
            }
        }
        this.curSlide = this.slides[this.idxSlide].clone();
        this.show();
    },
    show: function() {
        var slide = this.slideIn.getElement('div');
        if (slide) {
            slide.replaceWith(this.curSlide);
        } else {
            this.curSlide.injectInside(this.slideIn);
        }
        this.doEffect();
    },
    doEffect: function() {
        this.fxOn = true;
        var d = this.isFirst ? 0 : this.options.duration;
        var t = this.options.transition;

        var fxObj = this.slideIn.effects({
            duration: d,
            transition: t
        });
        var inX = 0;
        var inY = 0;
        var outX = 0;
        var outY = 0;
        var ww = this.wrapper.getStyle('width').toInt();
        var wh = this.wrapper.getStyle('height').toInt();
        if (this.step > 0) {
            if (this.options.direction == 'h') {
                inX = -ww;
                outX = ww;
            } else {
                inY = -wh;
                outY = wh;
            }
        } else {
            if (this.options.direction == 'h') {
                inX = ww;
                outX = -ww;
            } else {
                inY = wh;
                outY = -wh;
            }
        }
        if (this.isFirst) {
            if (this.auto) {
                this.step = 1;
            }
            this.isFirst = false;
        }
        fxObj.start({
            top: [inY, 0],
            left: [inX, 0],
            opacity: [1, 1]
        });
        this.slideOut.effects({
            duration: d,
            transition: t
        }).start({
            top: [0, outY],
            left: [0, outX]
        });

        this.fxEnd.delay(d + 75, this);
    },
    fxEnd: function() {
        this.fxOn = false;
        this.swapSlides();
        if (this.auto) {
            $clear(this.timer);
            this.timer = this.load.delay(this.options.delay, this);
        }
    },
    stop: function() {
        $clear(this.timer);
        this.auto = false;
    },
    play: function() {
        if (!this.auto) {
            $clear(this.timer);
            this.auto = true;
            this.step = 1;
            if (!this.fxOn) {
                this.load();
            }
        }
    },
    next: function() {
        this.stop();
        if (this.fxOn) { return; }
        this.step = 1;
        this.load();
    },
    prev: function() {
        this.stop();
        if (this.fxOn) { return; }
        this.step = -1;
        this.load()
    },
    swapSlides: function() {
        this.slideOut.setStyles({
            zIndex: 0,
            opacity: 0
        });
        var t = this.slideOut;
        this.slideOut = this.slideIn;
        this.slideIn = t;
    }
});
QScroller.implement(new Options, new Events);