Javascript for hierarchical data

I have web project which display parent and child data on a single gridview. Parent row contains key data and other data and on child rows key data are hidden and only other data are displayed.
Both parent and child rows contain a dropdownbox. If the dropdownlist on Parent row chnages I want to display the same value on child rows.

I have added the function as an attribute
ddlChoice.Attributes.Add(“onchange”, “parentChoice();”);

function is
function parentChoice()
{

var parentChoice= event.srcElement;
var keyVal = parentChoice.keyVal;
var choice = document.getElementsByTagName(“select”);

for(var i=0;i<choice.length;i++)
{
if(choice[i].keyVal && choice[i] != parentChoice && choice[i].keyVal == keyVal)
{
choice[i].selectedIndex = parentChoice.selectedIndex;
}
}
}

I dont get the childrows. How do I do this?

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