function jsScrollbar (o, s, a, ev) {
    var self = this;
    this.reset = function () {
        this._parent = o;
        this._src    = s;
        this.auto    = a ? a : false;
        this.eventHandler = ev ? ev : function () {};
        this._up   = this._findComponent("Scrollbar-Up", this._parent);
        this._down = this._findComponent("Scrollbar-Down", this._parent);
        this._yTrack  = this._findComponent("Scrollbar-Track", this._parent);
        this._yHandle = this._findComponent("Scrollbar-Handle", this._yTrack);
        this._trackTop = findOffsetTop(this._yTrack);
        this._trackHeight  = this._yTrack.offsetHeight;
        this._handleHeight = this._yHandle.offsetHeight;
        this._x = 0;
        this._y = 0;
        this._scrollDist  = 5;
        this._scrollTimer = null;
        this._selectFunc  = null;
        this._grabPoint   = null;
        this._tempTarget  = null;
        this._tempDistX   = 0;
        this._tempDistY   = 0;
        this._disabled    = false;
        this._ratio = (this._src.totalHeight - this._src.viewableHeight)/(this._trackHeight - this._handleHeight);
        this._yHandle.ondragstart  = function () {return false;};
        this._yHandle.onmousedown = function () {return false;};
        this._addEvent(this._src.content, "mousewheel", this._scrollbarWheel);
        this._removeEvent(this._parent, "mousedown", this._scrollbarClick);
        this._addEvent(this._parent, "mousedown", this._scrollbarClick);
        this._src.reset();
        with (this._yHandle.style) {
            top  = "0px";
            left = "0px";
        }
        this._moveContent();
        if (this._src.totalHeight < this._src.viewableHeight) {
            this._disabled = true;
            this._yHandle.style.visibility = "hidden";
            if (this.auto) this._parent.style.visibility = "hidden";
        } else {
            this._disabled = false;
            this._yHandle.style.visibility = "visible";
            this._parent.style.visibility  = "visible";
        }
    };
    this._addEvent = function (o, t, f) {
        if (o.addEventListener) o.addEventListener(t, f, false);
        else if (o.attachEvent) o.attachEvent('on'+ t, f);
        else o['on'+ t] = f;
    };
    this._removeEvent = function (o, t, f) {
        if (o.removeEventListener) o.removeEventListener(t, f, false);
        else if (o.detachEvent) o.detachEvent('on'+ t, f);
        else o['on'+ t] = null;
    };
    this._findComponent = function (c, o) {
        var kids = o.childNodes;
        for (var i = 0; i < kids.length; i++) {
            if (kids[i].className && kids[i].className == c) {
                return kids[i];
            }
        }
    };
    function findOffsetTop (o) {
        var t = 0;
        if (o.offsetParent) {
            while (o.offsetParent) {
                t += o.offsetTop;
                o  = o.offsetParent;
            }
        }
        return t;
    };
    this._scrollbarClick = function (e) {
        if (self._disabled) return false;
        e = e ? e : event;
        if (!e.target) e.target = e.srcElement;
        if (e.target.className.indexOf("Scrollbar-Up") > -1) self._scrollUp(e);
        else if (e.target.className.indexOf("Scrollbar-Down") > -1) self._scrollDown(e);
        else if (e.target.className.indexOf("Scrollbar-Track") > -1) self._scrollTrack(e);
        else if (e.target.className.indexOf("Scrollbar-Handle") > -1) self._scrollHandle(e);
        self._tempTarget = e.target;
        self._selectFunc = document.onselectstart;
        document.onselectstart = function () {return false;};
        self.eventHandler(e.target, "mousedown");
        self._addEvent(document, "mouseup", self._stopScroll, false);
        return false;
    };
    this._scrollbarDrag = function (e) {
        e = e ? e : event;
        var t = parseInt(self._yHandle.style.top);
        var v = e.clientY + document.body.scrollTop - self._trackTop;
        with (self._yHandle.style) {
            if (v >= self._trackHeight - self._handleHeight + self._grabPoint)
                top = self._trackHeight - self._handleHeight +"px";
            else if (v <= self._grabPoint) top = "0px";
            else top = v - self._grabPoint +"px";
            self._y = parseInt(top);
        }
        self._moveContent();
    };
    this._scrollbarWheel = function (e) {
        e = e ? e : event;
        var dir = 0;
        if (e.wheelDelta >= 120) dir = -1;
        if (e.wheelDelta <= -120) dir = 1;
        self.scrollBy(0, dir * 20);
        e.returnValue = false;
    };
    this._startScroll = function (x, y) {
        this._tempDistX = x;
        this._tempDistY = y;
        this._scrollTimer = window.setInterval(function () {
            self.scrollBy(self._tempDistX, self._tempDistY);
        }, 40);
    };
    this._stopScroll = function () {
        self._removeEvent(document, "mousemove", self._scrollbarDrag, false);
        self._removeEvent(document, "mouseup", self._stopScroll, false);
        if (self._selectFunc) document.onselectstart = self._selectFunc;
        else document.onselectstart = function () { return true; };
        if (self._scrollTimer) window.clearInterval(self._scrollTimer);
        self.eventHandler (self._tempTarget, "mouseup");
    };
    this._scrollUp = function (e) {this._startScroll(0, -this._scrollDist);};
    this._scrollDown = function (e) {this._startScroll(0, this._scrollDist);};
    this._scrollTrack = function (e) {
        var curY = e.clientY + document.body.scrollTop;
        this._scroll(0, curY - this._trackTop - this._handleHeight/2);
    };
    this._scrollHandle = function (e) {
        var curY = e.clientY + document.body.scrollTop;
        this._grabPoint = curY - findOffsetTop(this._yHandle);
        this._addEvent(document, "mousemove", this._scrollbarDrag, false);
    };
    this._scroll = function (x, y) {
        if (y > this._trackHeight - this._handleHeight)
            y = this._trackHeight - this._handleHeight;
        if (y < 0) y = 0;
        this._yHandle.style.top = y +"px";
        this._y = y;
        this._moveContent();
    };
    this._moveContent = function () {
        this._src.scrollTo(0, Math.round(this._y * this._ratio));
    };
    this.scrollBy = function (x, y) {
        this._scroll(0, (-this._src._y + y)/this._ratio);
    };
    this.scrollTo = function (x, y) {
        this._scroll(0, y/this._ratio);
    };
    this.swapContent = function (o, w, h) {
        this._removeEvent(this._src.content, "mousewheel", this._scrollbarWheel, false);
        this._src.swapContent(o, w, h);
        this.reset();
    };
    this.reset();
};