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?

seems by now (2014), we no longer get this error. Much easier to use. — gfaceless, Apr 10 '14 at 13:06

score 108 · Accepted Answer · edited Dec 10 '12 at 01:25

108

This should work:

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

edited Dec 10 '12 at 01:25

Logan

10,649
13
41
54

answered Feb 21 '11 at 20:52

Chetan

46,743
31
106
145

- if (isset(username))' isset is not defined – mbecker Feb 21 '11 at 21:08
2

Sorry, I got confused with PHP and Javascript. Updated my answer. – Chetan Feb 21 '11 at 21:30
7

Tanks a lot! This Code works: - if (typeof username !== "undefined") – mbecker Feb 21 '11 at 21:46

score 94 · Answer 2 · edited Sep 06 '12 at 01:25

94

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.

edited Sep 06 '12 at 01:25

broofa

37,461
11
73
73

answered Jun 13 '12 at 12:54

BMiner

16,669
12
53
53

This gives me a compiler error : 'builtin_function_or_method' object has no attribute 'username' – zakdances Feb 06 '13 at 10:11
@yourfriendzak - Are you sure your error is caused by this portion of your template? – BMiner Feb 07 '13 at 15:05
1

Works perfect and it's better than using inline javascript, thanks. – Sergi Ramón Feb 12 '13 at 11:54
I like this answer because this shows that Jade is whitespace sensitive language. – Victor.Palyvoda Sep 25 '14 at 15:51
Careful this will only work if the variable was defined in the controller at the `render` stage: `res.render('view', {username: user.name});` – Augustin Riedinger Apr 24 '17 at 15:35

score 9 · Answer 3 · answered May 23 '13 at 14:30

9

if 'username' in this
    p=username

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

answered May 23 '13 at 14:30

avoid3d

620
6
12

score 6 · Answer 4 · answered Jun 13 '12 at 13:45

6

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. :)

answered Jun 13 '12 at 13:45

Dominic Barnes

28,083
8
65
90

2

Thanks, though FYI for express 3.x this is now `app.locals({ username: false });` – 7zark7 Nov 09 '13 at 10:03
6

Nice approach. Note that in Express 4.x `app.locals` is not a function anymore so it should be `app.locals.username = false;` – Tom May 12 '14 at 12:02

score 1 · Answer 5 · answered May 10 '21 at 02:59

1

Even simpler with pug, the successor to jade

if msg
  p= msg

answered May 10 '21 at 02:59

I Like

1,711
2
27
52

score 0 · Answer 6 · answered Apr 24 '17 at 15:38

0

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();
};

answered Apr 24 '17 at 15:38

Augustin Riedinger

20,909
29
133
206

score 0 · Answer 7 · answered Feb 21 '11 at 20:45

0

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

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

answered Feb 21 '11 at 20:45

TK-421

10,598
3
38
34

Yes, but it still shouldn't return `undefined` if it's checked with `if` beforehand. – JohnAllen Mar 10 '11 at 19:23

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

7 Answers7

Linked