ASPX/.NET - "User.Identity.Name" any known issues?

I am building an intranet website. It should be JavaScript-html.
However, I have to check who is current windows domain-user logged in. So for my homepage, I have written aspx-page - myfirstpage.aspx (Because in JavaScript there is no way to find out currently logged-in user )  
So I am planning to get userid by using this code -

String username = User.Identity.Name; /// in myfirstpage.aspx.cs

Are there any problems/issues like browser issues in getting username like this in aspx?

Or is there any other way to get username using JavaScript...

thanks a lot...