Get the LoggedIn User ID from Sharepoint using Javascript

I had a task to create a silverlight application which can be inserted to a sharepoint webpart (Content Editor); Everything went fine, except getting the logged in user name in the sharepoint site.
It took a long time for me to find the solution, So I thought I can post it here so that it would be helpful for others

I used a javascript with the silverlight object to retrieve the user name

function GetSPUserId(){
return _spUserId.toString();
}


_spUserId returns the ID; from this you can easjavascript:void(0)
Save Nowily retrieve the user details;

To call this javascript in Silverlight application

string g_SPUserID = HtmlPage.Window.Invoke("GetSPUserId", null) as string;