How can I get a bound control's client ID with javascript and/or server-side tags?

Question

<asp:DataGrid>
    <ItemTemplate>
        1)
        <asp:TextBox ID="tbComments" onChange="javascript:checkLength(<%# tbComments.ClientId %>);" runat="server"/>
        2)
        <span id="<%# tbComments.ClientId %>Label"></span>
    </ItemTemplate>
</asp:DataGrid>

Any ideas to make the above working (which doesn't :P)?

Answer 1

Change your markup to pass "this" as a reference to the given comments box.

<asp:TextBox ID="tbComments" 
           onChange="javascript:checkLength(this);" runat="server"/>

Then in your checkLength() function, "e" is a direct reference to the DOM element that raised the onchange event.

function checkLength(e){
  alert(e.id); //id of the comments box
  //get a reference to the span element immediately after the textbox
  theSpan = e.parentNode.getElementsByTagName("span")[0];
  theSpan.innerHTML = "comments length: " + e.value.length;
}

Answer 2

Are you sure the problem isn't just the mispelling of "ClientId" in the following tag? :-)

<span id="<%# tbComments.CliendId %>Label"></span>

Answer 3

Is there something wrong with your JavaScript checkLength() function not appending Label to the Client ID? Then have your Javascript take both?:

<asp:DataGrid>
    <ItemTemplate>
        1)
        <asp:TextBox ID="tbComments"
            onChange="javascript:checkLength(<%# tbComments.ClientId %>, <%# tbComments.ClientId %>Label);"
            runat="server"/>
        2)
        <span id="<%# tbComments.ClientId %>Label"></span>
    </ItemTemplate>
</asp:DataGrid>

Answer 4

Just add a class to the span or the textbox and use jQuery to find the element in the dom and add a change event to the textbox run the checkLength code

$(document).ready(function()
{
    $('.myClass').change(function()
    {
         // do your length check...
    });
});