Asp.Net 2.0 Treeview Checkbox Check/Uncheck All script

Its a very common requirement to have the parent-child check behaviour in asp.net treeview. To define the problem:
1)Check all the child nodes if the parent is checked and uncheck all child nodes if parent is unchecked ( well, this part is simple).
2)If a node at any level is checked and all its siblings are already checked then the parent node should be checked and the same should apply for the parent node(i.e., if its siblings are checked....), this should happen till the root node.
3)If a node at any level is unchecked then the parents( ma, grand ma, grand grand ma....) up to the root node must be unchecked.

Well there have been scripts on the net that only half accomplished the task(check footnotes). So I wrote the script that solves the problem completely, upto best of my knowledge. I've tested in IE 7 and Firefox 2.0, hope it works fine for you all.

Here's how to implement it:

Step 1: In the page load in code behind file add an attribute to the treeview as:

If(!isPostBack)
{
    TreeView1.Attributes.Add("onclick","OnTreeClick(event)");
}

The desired affect could also be accomplished by direclty adding the attribute to the treeview tag in .aspx file as: <asp:treeview onclick="OnTreeClick(event)"... which would cause Visual Studio to display a warning but it works anyway but the codebehind way of doint it is the right way.

Step 2: Put the below script in the head section of your .aspx page:

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function OnTreeClick(evt)
{
 var src = window.event != window.undefined ? window.event.srcElement : evt.target;
 var isChkBoxClick = (src.tagName.toLowerCase() == "input" && src.type == "checkbox");
 if(isChkBoxClick)
 {
     var parentTable = GetParentByTagName("table", src);
     var nxtSibling = parentTable.nextSibling;
     //check if nxt sibling is not null & is an element node
      if(nxtSibling && nxtSibling.nodeType == 1)
     {
         if(nxtSibling.tagName.toLowerCase() == "div") //if node has children
         {
             //check or uncheck children at all levels
             CheckUncheckChildren(parentTable.nextSibling, src.checked);
         }
     }
 //check or uncheck parents at all levels
 CheckUncheckParents(src, src.checked);
 }
}

 function CheckUncheckChildren(childContainer, check)
{
 var childChkBoxes = childContainer.getElementsByTagName("input");
      var childChkBoxCount = childChkBoxes.length;
 for(var i=0;i<childChkBoxCount;i++)
 {
     childChkBoxes[i].checked = check;
 }
}

function CheckUncheckParents(srcChild, check)
{
 var parentDiv = GetParentByTagName("div", srcChild);
 var parentNodeTable = parentDiv.previousSibling;
 if(parentNodeTable)
 {
     var checkUncheckSwitch;
     if(check) //checkbox checked
     {
         var isAllSiblingsChecked = AreAllSiblingsChecked(srcChild);
         if(isAllSiblingsChecked)
                 checkUncheckSwitch = true;
         else
                 return; //do not need to check parent if any(one or more) child not checked
     }
     else //checkbox unchecked
     {
         checkUncheckSwitch = false;
     }
   
     var inpElemsInParentTable = parentNodeTable.getElementsByTagName("input");
     if(inpElemsInParentTable.length > 0)
     {
         var parentNodeChkBox = inpElemsInParentTable[0];
         parentNodeChkBox.checked = checkUncheckSwitch;
         //do the same recursively
        CheckUncheckParents(parentNodeChkBox, checkUncheckSwitch);
     }
 }
}

function AreAllSiblingsChecked(chkBox)
{
 var parentDiv = GetParentByTagName("div", chkBox);
 var childCount = parentDiv.childNodes.length;
 for(var i=0;i<childCount;i++)
 {
     if(parentDiv.childNodes[i].nodeType == 1)
     {
         //check if the child node is an element node
         if(parentDiv.childNodes[i].tagName.toLowerCase() == "table")
         {
             var prevChkBox = parentDiv.childNodes[i].getElementsByTagName("input")[0];
             //if any of sibling nodes are not checked, return false
             if(!prevChkBox.checked)
             {
                 return false;
             }
         }
     }
 }
 return true;
}

//utility function to get the container of an element by tagname
function GetParentByTagName(parentTagName, childElementObj)
{
 var parent = childElementObj.parentNode;
 while(parent.tagName.toLowerCase() != parentTagName.toLowerCase())
     {
         parent = parent.parentNode;
     }
 return parent;
}

Get Formatted Version Of Above Script

The script is pretty much self explanatory with function names saying it all.
Comments awaited.

Footnotes: There has been other scripts on the net that accomplished the job only partially, the one that reached closest to doing it could be found in this thread on asp.net forums, i too have posted my solution there.