I am unable to understand this code.
$rootScope.loginbtn=$sessionStorage.loginbtn;
$rootScope.userName=$sessionStorage.userName;
$rootScope.admin=$sessionStorage.admin
You have not given many details so an answer will be hard to give.
From what I can see though, $sessionStorage is a Angular service that acts as a wrapper for the inbuilt browser sessionStorage.
The code is making the login button, username and admin available on the $rootScope, presumably so they can be accessed in other controllers within the app.
Provide more details though, and we can give you a better answer