Copy values based on checkbox with JavaScript

I saw this in another post but can't seem to get it to work.  I tried to set a breakpoint in VS 2008 at function copyAddress() but it does not appear to be getting hit when I check my checkbox.

In my .aspx I have the following Javascript:

function copyAddress()
{
    var chkSameAddress = document.getElementById('<%= chkbxDeliveryAddrSame.ClientID %>');
    var txtStreet = document.getElementById('<%= txtStreet.ClientID %>');
    var txtDeliveryStreet = document.getElementById(' <%= txtDeliveryStreet.ClientID %>');
    var txtZip = document.getElementById('<%= txtZip.ClientID %>');
    var txtDeliveryZip = document.getElementById('<%= txtDeliveryZip.ClientID %>');
    var ddlCity = document.getElementById('<%= ddlDeliveryCity.ClientID %>');
    var ddlDeliveryCity = document.getElementById('<%= ddlDeliveryCity.ClientID %>');

    if(chkSameAddress.checked)
    {
        txtDeliveryStreet.value = txtStreet.value;
        txtDeliveryZip.value = txtZip.value;
        ddlDeliveryCity.value = ddlCity.value;
    }
    else
    {
        txtDeliveryStreet.value=' ';
        txtDeliveryZip.value=' ';
        ddlDeliveryCity.value = 0;
    }
}  

 

In my code-behind I have:

chkbxDeliveryAddrSame.Attributes.Add("OnCheckedChanged", "javascript:return copyAddress();");

 

When I view source, I see:

function copyAddress()
{
    var chkSameAddress = document.getElementById('ctl00_ContentPlaceHolder_MainBody_chkbxDeliveryAddrSame');
    var txtStreet = document.getElementById('ctl00_ContentPlaceHolder_MainBody_txtStreet');
    var txtDeliveryStreet = document.getElementById(' ctl00_ContentPlaceHolder_MainBody_txtDeliveryStreet');
    var txtZip = document.getElementById('ctl00_ContentPlaceHolder_MainBody_txtZip');
    var txtDeliveryZip = document.getElementById('ctl00_ContentPlaceHolder_MainBody_txtDeliveryZip');
    var ddlCity = document.getElementById('ctl00_ContentPlaceHolder_MainBody_ddlDeliveryCity');
    var ddlDeliveryCity = document.getElementById('ctl00_ContentPlaceHolder_MainBody_ddlDeliveryCity');

    if(chkSameAddress.checked)
    {
        txtDeliveryStreet.value = txtStreet.value;
        txtDeliveryZip.value = txtZip.value;
        ddlDeliveryCity.value = ddlCity.value;
    }
    else
    {
        txtDeliveryStreet.value=' ';
        txtDeliveryZip.value=' ';
        ddlDeliveryCity.value = 0;
    }
}

 

<span OnCheckedChanged="javascript:return copyAddress();"><input id="ctl00_ContentPlaceHolder_MainBody_chkbxDeliveryAddrSame" type="checkbox" name="ctl00$ContentPlaceHolder_MainBody$chkbxDeliveryAddrSame" /></span>

I'm not good with JavaScript so wondering what I am missing here or doing wrong.  I'll continue to research.