How do I access a textbox in an asp GridView

[Ellary Kahan]

I am using the following code:

function ZeroASN() {
      if (document.getElementById("ddlheadexempcode").selectedIndex == "0")
      { document.getElementById("lblError").innerHTML = "Reason code must be entered."; }
      else {
        var x = document.getElementById("GridDetail").rows
        var z=x.length
        for (i = 1; i <= z; i++) {
          var y = document.getElementById("GridDetail").rows[i].cells;
          y[21].document.getElementById("<%= txtRevAsn.ClientID =%>").value = "0.00"; 
        }
        document.getElementById("lblError").innerHTML = " ";
      }
    }
 

The bolded statement beginning "y[21]" is the one I'm having trouble with. The one here gives me an error that txtRevASN is undefined. This is true, as it has "GridDetail" appended as a prefix plus something else.
I've tried

y[21].firstChild.value = "0.00"
 

But this doesn't seem to work.

The following works but blows away the text box.

y[21].innerHTML= "0.00"
 

So how do I reference the textbox?
Thank you.

[gits]

if your node y[21] has exactly one textbox as a childnode then you might use something like the following:

var childNodes = y[21].childNodes;
 
for (var i = 0, l = childNodes.length; i < l; i++) {
    var node = childNodes[i];
 
    if (node.tagName != 'INPUT') {
        continue;
    } else {
        node.value = '0.00';
    }
}

[Ellary Kahan]

Thank you. That worked.

[Ellary Kahan]

I keep getting an error on this statement:
var y = x.rows[i].cells;
The code does work.
Is there a correct way to do this? Or is this error caused by the fact that i is not defined until the code executes?

[gits]

?? where does this code come from and what should it do?

[Ellary Kahan]

I found the error. I was setting z to the length of the array and in the for loop I set the subscript <= z when it should have been < z.
Thanks.