//Create an array 
var allPageTags = new Array(); 

function doSomethingWithClasses(theClass) {
//Populate the array with all the page tags
var allPageTags=document.getElementsByTagName("*");
//Cycle through the tags using a for loop
for (i=0; i<allPageTags.length; i++) {
//Pick out the tags with our class name
if (allPageTags[i].className==theClass) {
//Manipulate this in whatever way you want
return allPageTags[i];
}
}
} 

function toggleLayer( whichLayer )
{
  var elem, vis;
  elem = doSomethingWithClasses(whichLayer);
  vis = elem.style;
  // if the style.display value is blank we try to figure it out here
  if(vis.display==''&&elem.offsetWidth!=undefined&&elem.offsetHeight!=undefined)
    vis.display = (elem.offsetWidth!=0&&elem.offsetHeight!=0)?'block':'none';
  vis.display = (vis.display==''||vis.display=='block')?'none':'block';
}