Find Server Side Dynamic Controls in asp Table through Javascript

Hi Everyone....
I have a asp table on my web page which is using Master page and on Page Load I am generating few dynamic textboxes. I want to update the values of those textboxes using Javascript. It seems I have tried all the tricks in the trade with no success. Check out the code below..
 
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
    <script language = "javascript" type = "text/javascript">       
            function FindTextBox() {
                for (var i = 0; i <= 4; i++) {
                    var txt = document.getElementById("txt" + i) ...