Technique SCR33:Using script to scroll content, and providing a mechanism to pause it

Example 1

In this example CSS and Javascript are used to visually present some text in a scrolling format. A link is included to pause the scrolling movement.

This implementation will display the full text and omit the link when Javascript or CSS are unsupported or inactive.

The following code is an amended version of webSemantic's Accessible Scroller (as at July 2008).

The XHTML component:

...
<div id="scroller">
<p id="tag">This text will scroll and a Pause/Scroll link will be present 
when Javascript and CSS are supported and active.</p>
</div>
...

The CSS component:

...
body {font:1em verdana,sans-serif; color:#000; margin:0}

/* position:relative and overflow:hidden are required */
#scroller { position:relative; overflow:hidden; width:15em; border:1px solid #008080; }

/* add formatting for the scrolling text */
#tag { margin:2px 0; }

/* #testP must also contain all text-sizing properties of #tag  */
#testP { visibility:hidden; position:absolute; white-space:nowrap; } 

/* used as a page top marker and to limit width */
#top { width:350px; margin:auto; }
...

The JavaScript component:

var speed=50        // speed of scroller
var step=3          // smoothness of movement
var StartActionText= "Scroll"  // Text for start link
var StopActionText = "Pause"   // Text for stop link

var x, scroll, divW, sText=""

function onclickIE(idAttr,handler,call){
  if ((document.all)&&(document.getElementById)){idAttr[handler]="Javascript:"+call}
}

function addLink(id,call,txt){
  var e=document.createElement('a')
  e.setAttribute('href',call)
  var linktext=document.createTextNode(txt)
  e.appendChild(linktext)
  document.getElementById(id).appendChild(e)
}

function getElementStyle() {
    var elem = document.getElementById('scroller');
    if (elem.currentStyle) {
        return elem.currentStyle.overflow;
    } else if (window.getComputedStyle) {
        var compStyle = window.getComputedStyle(elem, '');
        return compStyle.getPropertyValue("overflow");
    }
    return "";
}

function addControls(){
// test for CSS support first 
// test for the overlow property value set in style element or external file
if (getElementStyle()=="hidden") {
  var f=document.createElement('div');
  f.setAttribute('id','controls');
  document.getElementById('scroller').parentNode.appendChild(f);
  addLink('controls','Javascript:clickAction(0)',StopActionText);
  onclickIE(document.getElementById('controls').childNodes[0],"href",'clickAction(0)');
  document.getElementById('controls').style.display='block';
  }
}

function stopScroller(){clearTimeout(scroll)}

function setAction(callvalue,txt){
  var c=document.getElementById('controls')
  c.childNodes[0].setAttribute('href','Javascript:clickAction('+callvalue+')')
  onclickIE(document.getElementById('controls').childNodes[0],"href",'clickAction

('+callvalue+')')
  c.childNodes[0].firstChild.nodeValue=txt
}

function clickAction(no){
  switch(no) {
    case 0:
      stopScroller();
      setAction(1,StartActionText);
      break;
    case 1:
      startScroller();
      setAction(0,StopActionText);
  }
}

function startScroller(){
  document.getElementById('tag').style.whiteSpace='nowrap'
  var p=document.createElement('p')
  p.id='testP'
  p.style.fontSize='25%' //fix for mozilla. multiply by 4 before using
  x-=step
  if (document.getElementById('tag').className) p.className=document.getElementById

('tag').className
  p.appendChild(document.createTextNode(sText))
  document.body.appendChild(p)
  pw=p.offsetWidth
  document.body.removeChild(p)
  if (x<(pw*4)*-1){x=divW}
  document.getElementById('tag').style.left=x+'px'
  scroll=setTimeout('startScroller()',speed)
}

function initScroller(){
  if (document.getElementById && document.createElement && document.body.appendChild) {
    addControls();
    divW=document.getElementById('scroller').offsetWidth;
    x=divW;
    document.getElementById('tag').style.position='relative';
    document.getElementById('tag').style.left=divW+'px';
    var ss=document.getElementById('tag').childNodes;
    for (i=0;i<ss.length;i++) {sText+=ss[i].nodeValue+" "};
    scroll=setTimeout('startScroller()',speed);
  }
}

function addLoadEvent(func) {
  if (!document.getElementById | !document.getElementsByTagName) return
  var oldonload = window.onload
  if (typeof window.onload != 'function') {
    window.onload = func;
  } else {
    window.onload = function() {
      oldonload()
      func()
    }
  }
}

addLoadEvent(initScroller)

A working example of this code, Example of using script to scroll content and providing a mechanism to pause it, is available.