Jade - Silnik szablonów: Jak sprawdzić, czy istnieje zmienna

Obecnie używam Jade w nowym projekcie. Chcę wyrenderować stronę i sprawdzić, czy jest dostępna określona zmienna.

app.js:

app.get('/register', function(req, res){
    res.render('register', {
        locals: {
          title: 'Register',
          text: 'Register as a user.',
        }
      });
});

register.jade:

- if (username)
p= username
- else
p No Username!

I always get the following error:

username is not defined

Any ideas on how I can fix this?

This should work:

- if (typeof(username) !== 'undefined'){
  //-do something
-}

Simpler than @Chetan's method if you don't mind testing for falsy values instead of undefined values:

if locals.username
  p= username
else
  p No Username!

This works because the somewhat ironically named locals is the root object for the template.

if 'username' in this
    p=username

This works because res.locals is the root object in the template.

If you know in advance you want a particular variable available, but not always used, I've started adding a "default" value to the helpers object.

app.helpers({ username: false });

This way, you can still do if (username) { without a catastrophic failure. :)

Shouldn't 'username' be included in the locals object?

https://github.com/visionmedia/jade/tree/master/examples

Created a middleware to have the method isDefined available everywhere in my views:

module.exports = (req, res, next) => {
  res.locals.isDefined = (variable) => {
    return typeof(variable) !== 'undefined'
  };  
  next();
};