call asp.net objects in javascript

Hi

Generally we are calling ASP.NET controls in javascript like

<SCRIPT LANGUAGE="JAVASCRIPT">
function getValue()
{
    var id1=document.getElementById("<%= txtUsername.ClientID %>");
}
</SCRIPT>
<form>
<asp:textbox id="txtUsername" runat="server"></asp:textbox>
</form>
In the above case if we write both asp.net and javascript in the same page the above code works fine. if we write javascirpt code in another page, the clientid is not working, is there any another method to call?

Thanks
Hemadri

.js files are not parsed in the same way as aspx so the "<%= txtUsername.ClientID %>" expresion is not evaluated.  if you want to move your javscript to an seperate file, you have to leave the portions that extract the clientID on the ASPX page that declares the control and then use that to set the values into some storage that your .js file can use. 

PerfectPhase said:

.js files are not parsed in the same way as aspx so the "<%= txtUsername.ClientID %>" expresion is not evaluated.  if you want to move your javscript to an seperate file, you have to leave the portions that extract the clientID on the ASPX page that declares the control and then use that to set the values into some storage that your .js file can use.