Conditionals in Pug can evaluate statements in a manner similar to JavaScript. You can evaluate variables created in Pug, or those passed to it by your route (res.render, pug.renderFile, etc).

index.js

var authorized = true
res.render("index", {
    authorized: authorized
});

index.pug

- var showLogin = false;
if authorized && showLogin === true
    .welcome Welcome back to our website!
else
    .login
        a(href="/login") Login

index.pug output

<div class="login"><a href="/login">Login</a></div>

You can choose to prepend an if or else operator with a dash, but it is not necessary. You will need to wrap the statement in parentheses, though (if you omit a dash, you do not need parentheses.)

- var showLogin = false;
- if (showLogin === true)
    .welcome Welcome back to our website!
- else
    .login
        a(href="/login") Login

index.pug output

<div class="login"><a href="/login">Login</a></div>

You can chain any number of else if statements to an existing if statement, to evaluate a sequence of statements.

index.pug

- var page = 60;
if page => 52
    h1 Lots of numbers!
else if page > 26 && page < 52
    h1 A few numbers
else
    h1 Not a lot of numbers

index.pug output

<h1>Lots of numbers!</h1>

unless is the inverse operation of if in Pug. It is analogous to if !(statement).

index.pug

- var likesCookies = true;
unless likesCookies === true
    h2 You don't like cookies :(
else
    h2 You like cookies!

index.pug output

<h1>You like cookies!</h1>

Note: else unless statements do not work with unless; you can chain an else if statement to an unless statement, but else unless does not work.