Get value of the textbox for the hiddenfield value that is saved/checkbox selected

I have a gridview which has a CHECKBOX, A HIDDEN FIELD AND A TEXTBOX.

When the checkbox is checked the Hiddenfield value gets saved in a list.

I need to know the value of the textbox field for the hiddenfield value that is saved/checkbox selected

Script which saves the hiddenfield value to list on checkbox check

<script type="text/javascript">
//Reference of the GridView. 
var TargetBaseControl = null;
//Total no of checkboxes in a particular column inside the GridView.
var CheckBoxes;
//Total no of checked checkboxes in a particular column inside the GridView.
var CheckedCheckBoxes;
//Array of selected item's Ids.
var SelectedItems;
//Hidden field that wil contain string of selected item's Ids separated by '|'.
var SelectedValues;

window.onload = function () {
    //Get reference of the GridView. 
    try {
        TargetBaseControl = document.getElementById('<%= this.GVWDLegalHold.ClientID %>');
    }
    catch (err) {
        TargetBaseControl = null;
    }

    //Get total no of checkboxes in a particular column inside the GridView.
    try {
        CheckBoxes = parseInt('<%= this.GVWDLegalHold.Rows.Count %>');
    }
    catch (err) {
        CheckBoxes = 0;
    }

    //Get total no of checked checkboxes in a particular column inside the GridView.
    CheckedCheckBoxes = 0;

    //Get hidden field that wil contain string of selected item's Ids separated by '|'.
    SelectedValues = document.getElementById('<%= this.hdnFldSelectedValuesWDhold.ClientID %>');

    //Get an array of selected item's Ids.
    if (SelectedValues.value == '')
        SelectedItems = new Array();
    else
        SelectedItems = SelectedValues.value.split('|');

    //Restore selected CheckBoxes' states.
    if (TargetBaseControl != null)
        RestoreState();
}

function HeaderClick(CheckBox) {
    //Get all the control of the type INPUT in the base control.
    var Inputs = TargetBaseControl.getElementsByTagName('input');

    //Checked/Unchecked all the checkBoxes in side the GridView & modify selected items array.
    for (var n = 0; n < Inputs.length; ++n)
        if (Inputs[n].type == 'checkbox' && Inputs[n].id.indexOf('chkSelectAddWDHold', 0) >= 0) {
            Inputs[n].checked = CheckBox.checked;
            //if (CheckBox.checked)
            //  SelectedItems.push(document.getElementById(Inputs[n].id.replace('chkSelectAdd', 'hdnFldId')).value);
            if (CheckBox.checked) {
                var strTempID = SelectedItems.push(document.getElementById(Inputs[n].id.replace
                    ('chkSelectAddWDHold', 'hdnFldIdapWDHold')).value);

                if (IsItemExists(strTempID) == -1) {
                    SelectedItems.push(strTempID);
                }
            }
            else
                DeleteItem(document.getElementById(Inputs[n].id.replace('chkSelectAddWDHold', 'hdnFldIdapWDHold')).value);
        }

    //Update Selected Values. 
    SelectedValues.value = SelectedItems.join('|');

    //Reset Counter
    CheckedCheckBoxes = CheckBox.checked ? CheckBoxes : 0;
}

function ChildClick(CheckBox, HCheckBox, Id) {
    //Modifiy Counter;            
    if (CheckBox.checked && CheckedCheckBoxes < CheckBoxes)
        CheckedCheckBoxes++;
    else if (CheckedCheckBoxes > 0)
        CheckedCheckBoxes--;

    //Change state of the header CheckBox.
    if (CheckedCheckBoxes < CheckBoxes)
        HCheckBox.checked = false;
    else if (CheckedCheckBoxes == CheckBoxes)
        HCheckBox.checked = true;

    //Modify selected items array.
    if (CheckBox.checked)
        SelectedItems.push(Id);
    else
        DeleteItem(Id);

    //Update Selected Values. 
    SelectedValues.value = SelectedItems.join('|');
}

function RestoreState() {
    //Get all the control of the type INPUT in the base control.
    var Inputs = TargetBaseControl.getElementsByTagName('input');

    //Header CheckBox
    var HCheckBox = null;

    //Restore previous state of the all checkBoxes in side the GridView.
    for (var n = 0; n < Inputs.length; ++n)
        if (Inputs[n].type == 'checkbox' && Inputs[n].id.indexOf('chkSelectAddWDHold', 0) >= 0)
            if (IsItemExists(document.getElementById(Inputs[n].id.replace('chkSelectAddWDHold', 'hdnFldIdapWDHold')).value) > -1) {
                Inputs[n].checked = true;
                CheckedCheckBoxes++;
            }
            else
                Inputs[n].checked = false;
        else if (Inputs[n].type == 'checkbox' && Inputs[n].id.indexOf('chkSelectAllWDHold', 0) >= 0)
            HCheckBox = Inputs[n];

    //Change state of the header CheckBox.
    if (CheckedCheckBoxes < CheckBoxes)
        HCheckBox.checked = false;
    else if (CheckedCheckBoxes == CheckBoxes)
        HCheckBox.checked = true;
}

function DeleteItem(Text) {
    var n = IsItemExists(Text);
    if (n > -1)
        SelectedItems.splice(n, 1);
}

function IsItemExists(Text) {
    for (var n = 0; n < SelectedItems.length; ++n)
        if (SelectedItems[n] == Text)
            return n;

    return -1;
}     
</script>