set focus to webcontrol on usercontrol in ASP.NET

I'm developing an webapplication with ASP.NET.

On the login page I would like to set the focus on the username textbox.

I have tried to use the javascript code like document.formname.textboxname.focus();.
This works when the textbox stands on the page.

But my textbox stands on a user control that stands on the page. When I try the code document.formname.usercontrolname.textboxname.focus();, it does not work. I don't get an error on the page.

Can somebody tell me what I do wrong or give an other solution?

Thank you

Anneke

.NET generate an ID like UserControlName_TextBoxName
try:
document.formname.usercontrolname_textboxname.focus()

Your suggestion works.

Thank you for your help.

Anneke