Use JavaScript expressions to decide which parts of a template should be rendered.

if user
  h1 Welcome, #{user.name}
else
  h1 Welcome, guest

else if

if account.isAdmin
  p Administrator
else if account.isMember
  p Member
else
  p Visitor

unless

unless provides a convenient way to express a negative condition.

unless user.isLoggedIn
  a(href="/login") Sign in

It is equivalent in meaning to testing the opposite condition with if. (source)