Jade - Template Engine: How to check if a variable exists

Question

I'm currently using Jade on a new project. I want to render a page and check if a certain variable is available.

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?

September

seems by now (2014), we no longer get this error. Much easier to use. – Christadelphian

Answer 1

This should work:

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

Allisonallissa

- if (isset(username))' isset is not defined – September

Sorry, I got confused with PHP and Javascript. Updated my answer. – Allisonallissa

Tanks a lot! This Code works: - if (typeof username !== "undefined") – September

Answer 2

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.

Weatherly

This gives me a compiler error : 'builtin_function_or_method' object has no attribute 'username' – Hinz

@yourfriendzak - Are you sure your error is caused by this portion of your template? – Weatherly

Works perfect and it's better than using inline javascript, thanks. – Phototonus

I like this answer because this shows that Jade is whitespace sensitive language. – Infecund

Careful this will only work if the variable was defined in the controller at the render stage: res.render('view', {username: user.name}); – Brandling

Answer 3

if 'username' in this
    p=username

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

Ideality

Answer 4

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. :)

Corrida

Thanks, though FYI for express 3.x this is now app.locals({ username: false }); – Premedical

Nice approach. Note that in Express 4.x app.locals is not a function anymore so it should be app.locals.username = false; – Cohby

Answer 5

Even simpler with pug, the successor to jade

if msg
  p= msg

Parkinson

Answer 6

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

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

Randolph

Yes, but it still shouldn't return undefined if it's checked with if beforehand. – Chance

Answer 7

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();
};

Brandling