Conditional Include in Jade + Express

How can one use if -else statement on "include" in jade??

For example, if I have two separate navigation bar templates navbar.jade and navbar_notloggedin.jade

I would like to do:

input(type='hidden', value= user.user)#username

- if(user.user!="")
  include navbar
- else if(user.user=="")
  include navbar_notloggedin 

You can use,

-if (user.user)
 include navbar
-else
 include navbar_notloggedin 

The if statement will check whether the variable is defined or not, not whether it is an empty string or not. However, I assume you are not storing empty string values for user.