Scroll div contents with Javascript.

I was asked to convert a flash site to html. Her flash site had images of arrows that controlled the scroll of her content, so, I was asked to reproduce that effect. Here is the code I wrote to create a custom scroll with javascript, which uses getElementById & .scrollTop. It is recommended that you initialize the scrolling div with the style of overflow: auto; thus, the user will still be able to scroll the div if they have javascript disabled.

Here's the css:

<style type="text/css">
  #scroll_up {
    cursor: pointer;
  }
  #scroll_down {
    cursor: pointer;
  }
  #scroll_box {
    height: 200px;
    width: 300px;
    overflow: auto;
  }
</style>

The javascript

// gives up and down scroll buttons to images, spans, ... named up_name, down_name, respectively.
// will keep the default scroll_box's style overflow if it encounters errors (so make overflow: auto;)

// usage: put this after the scrollbox div:  var div_scroll1 = new TextScroll('div_scroll1', 'scroll_box');
function TextScroll(scrollname, div_name, up_name, down_name)
{
    this.div_name = div_name;
    this.name = scrollname;
    this.scrollCursor = 0;
    this.speed = 5;
    this.timeoutID = 0;
    this.div_obj = null;
    this.up_name = up_name;
    this.dn_name = down_name;

{
        if (document.getElementById) {
            div_obj = document.getElementById(this.div_name);
            if (div_obj) {
                this.div_obj = div_obj;
                this.div_obj.style.overflow = 'hidden';
            }
            div_up_obj = document.getElementById(this.up_name);
            div_dn_obj = document.getElementById(this.dn_name);
            if (div_up_obj && div_dn_obj) {
                div_up_obj.setAttribute("onmouseover", scrollname + ".scrollUp();")
                div_up_obj.setAttribute("onmouseout", scrollname + ".stopScroll();")

div_dn_obj.setAttribute("onmouseover", scrollname + ".scrollDown();")
                div_dn_obj.setAttribute("onmouseout", scrollname + ".stopScroll();")
            }
        }
    }

this.stopScroll = function() {
        clearTimeout(this.timeoutID);
    }

this.scrollUp = function() {
        if (this.div_obj) {
            this.scrollCursor = (this.scrollCursor - this.speed) < 0 ? 0 : this.scrollCursor - this.speed;
            this.div_obj.scrollTop = this.scrollCursor;
            this.timeoutID = setTimeout(this.name + ".scrollUp()", 60);
        }
    }

this.scrollDown = function() {
        if (this.div_obj) {
            this.scrollCursor += this.speed;
            this.div_obj.scrollTop = this.scrollCursor;
            this.timeoutID = setTimeout(this.name + ".scrollDown()", 60);
        }
    }

this.resetScroll = function() {
        if (this.div_obj) {
            this.div_obj.scrollTop = 0;
            this.scrollCursor = 0;
        }
    }
}

usage example:

<span id="scroll_up">scroll up</span> | <span id="scroll_down">scroll down</span>
<br>
<div id="scroll_box">
  <p>a lot of content</p>
</div>

<script type="text/javascript">
  var div_scroll1 = new TextScroll('div_scroll1', 'scroll_box', 'scroll_up', 'scroll_down');
</script>

I hope this pasted right.