What is the proper way to check for existence of variable in an EJS template (using ExpressJS)?

Question

On the EJS github page, there is one and only one simple example: https://github.com/visionmedia/ejs

Example

<% if (user) { %>
    <h2><%= user.name %></h2>
<% } %>

This seems to be checking for the existence of a variable named user, and if it exists, do some stuff. Duh, right?

My question is, why in the world would Node throw a ReferenceError if the user variable doesn't exist? This renders the above example useless. What's the appropriate way to check for the existence of a variable? Am I expected to use a try/catch mechanism and grab that ReferenceError?

ReferenceError: user is not defined
    at IncomingMessage.anonymous (eval at <anonymous> (/usr/local/lib/node/.npm/ejs/0.3.1/package/lib/ejs.js:140:12))
    at IncomingMessage.<anonymous> (/usr/local/lib/node/.npm/ejs/0.3.1/package/lib/ejs.js:142:15)
    at Object.render (/usr/local/lib/node/.npm/ejs/0.3.1/package/lib/ejs.js:177:13)
    at ServerResponse.render (/usr/local/lib/node/.npm/express/1.0.7/package/lib/express/view.js:334:22)
    at Object.<anonymous> (/Users/me/Dropbox/Projects/myproject/server.js:188:9)
    at param (/usr/local/lib/node/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:146:21)
    at pass (/usr/local/lib/node/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:162:10)
    at /usr/local/lib/node/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:152:27
    at Object.restrict (/Users/me/Dropbox/Projects/myproject/server.js:94:5)
    at param (/usr/local/lib/node/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:146:21)

I understand that I could make this error go away by simply adding a "user" local variable in my server code, but the whole point here is that I want to check for the existence of such variables at runtime using your every day if/else nullcheck type pattern. An exception for a variable that doesn't exist seems ridiculous to me.

score 196 · Accepted Answer · edited May 31 '17 at 16:10

196

The same way you would do it with anything in js, typeof foo == 'undefined', or since "locals" is the name of the object containing them, you can do if (locals.foo). It's just raw js :p

edited May 31 '17 at 16:10

Bruiser

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answered Mar 21 '11 at 00:22

tjholowaychuk

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I'm beginning to wonder if I've got a bigger problem on my hands. This throws a Reference Error too: <% alert('test'); %> – Aashay Desai Mar 21 '11 at 00:34
2

@Aashay `alert` is part of a browser's `window` object, and not available in node.js. The alternative is `console.log`, though I don't know if it's available in an ejs template unless you pass it in via `locals`. – Zikes Mar 23 '11 at 17:10
2

@Zikes In this case I'm looking specifically for EJS, so it's on the browser page. But, like TJ said, typeof foo == 'undefined' works. I learned that I could also add a simple !!foo if foo has been defined but is null or empty. – Aashay Desai Jun 27 '11 at 06:23
24

Is there a shorthand for this? Why doesn't EJS simply honor the if (foo) case? – mattdlockyer Aug 22 '13 at 15:26
is locals.foo the same as foo? – OMGPOP Jun 21 '15 at 03:57
I have the same problem. I have to check if(locals.foo) instead of just checking if(foo). – Alexander Mills Aug 04 '15 at 20:48
10

`if (locals.user){ }` FTW – s2t2 Mar 28 '16 at 20:25
1

`<% if (locals.foo) { %> Here is the variable: <%= foo %> <% } %>` – stackunderflow Jan 19 '17 at 21:04
This is wrong. In ejs, if you do a type check or any check on an undefined variable, it throws an error. Every time. The above answer `typeof foo == 'undefined'` is incorrect. – Tyguy7 Mar 10 '20 at 22:16

score 49 · Answer 2 · answered Mar 24 '17 at 07:43

49

Try prepending the variable with locals

Example: if(locals.user){}

answered Mar 24 '17 at 07:43

spencer.sm

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score 33 · Answer 3 · answered Sep 11 '17 at 14:08

33

<% if (locals.user) { %>

 // Your logic goes here 

<% } %>

answered Sep 11 '17 at 14:08

Anirudh

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Paulius Uza · Answer 4 · 2014-01-21T16:11:21.223

14

You can create a view helper which checks for "obj === void 0", this one is for express.js:

res.locals.get = function() {
    var args = Array.prototype.slice.call(arguments, 0);
    var path = args[0].split('.');
    var root = this;
    for (var i = 0; i < path.length; i++) {
        if(root[path[i]] === void 0) {
            return args[1]?args[1]:null;
        } else {
            root = root[path[i]];
        }
    };
    return root;
}

Then use it in the view like

<%- get('deep.nested.non.existent.value') %>  //returns: null
<%- get('deep.nested.non.existent.value', "default value") %> //returns: default value

edited Jan 21 '14 at 16:11

answered Jan 21 '14 at 14:33

Paulius Uza

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not sure why this was downvoted, its rather elegant in my opinion. – joseym Jul 30 '15 at 15:40
What is the difference between `<%=` and `<%-`? – NobleUplift May 16 '19 at 16:10
2

@NobleUplift As per [the documentation](https://ejs.co/#docs), under "Tags": `<%=` HTML escapes the value first; `<%-` outputs the unescaped value. So `` would become a bold tag when using `<%-`, but simply the text "" when using `<%=` – Matheus Avellar Sep 03 '19 at 18:39
Thank you! I had no idea <%- was even a valid tag. – NobleUplift Sep 04 '19 at 02:18
1

I know it's a long dated post, but how can I implement this ? I tried on my own, but can't find how to properly convert this to a helper. thank you. – Jonathan Lafleur Sep 23 '20 at 19:40

score 12 · Answer 5 · answered Feb 19 '14 at 14:22

12

To check if user is defined, you need to do that:

<% if (this.user) { %>
   here, user is defined
<% } %>

answered Feb 19 '14 at 14:22

HenioJR

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This does not work in the most up-to-date EJS library (1.0.0). Although valid Javascript, EJS will refuse to act as expected. – Axoren Feb 22 '15 at 00:45
6

Does not work for me. Even though I have defined `foo`, else clause is still evaluated. Tested with EJS 2.3.4 EDIT: using `locals` in place of `this` works – X_Trust Feb 09 '16 at 21:21

score 9 · Answer 6 · answered Oct 17 '13 at 21:50

I've come across the same issue using node.js with mongoose/express/ejs when making a relation between 2 collections together with mongoose's populate(), in this case admins.user_id existed but was related to an inexistant users._id.
So, couldn't find why:

if ( typeof users.user_id.name == 'undefined' ) ...

was failing with "Cannot read property 'name' of null" Then I noticed that I needed to do the checking like this:

if ( typeof users.user_id == 'undefined' ) ...

I needed to check the "container" of 'name', so it worked!
After that, this worked the same:

if ( !users.user_id ) ...

Hope it helps.

Anyway, can't believe there so few official documentation on EJS... they don't update their [documentation](http://www.embeddedjs.com/) since 2010!!! — aesede, Jul 20 '15 at 14:06

score 4 · Answer 7 · answered Apr 08 '21 at 01:01

4

This may help somebody.

<p><%= locals?.message %></p>

or

<p><%= locals.message || '' %></p>

answered Apr 08 '21 at 01:01

viniciusalvess

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score 3 · Answer 8 · answered May 31 '18 at 23:32

3

Came to this page for an answer but I came up with a shorter inline syntax for it which is:

 <h2><%= user.name ? property.escrow.emailAddress : '' %></h2>

answered May 31 '18 at 23:32

Adam Boostani

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This is dangerous to use, because if the object 'user' does not have a 'name' property, the ejs rendering will fail. – Marko Rochevski Nov 01 '19 at 12:59

score 2 · Answer 9 · answered Jul 13 '16 at 13:18

What I do is just pass a default object I call 'data' = '' and pass it to all my ejs templates. If you need to pass real data to ejs template, add them as property of the 'data' object.

This way, 'data' object is always defined and you never get undefined error message, even if property of 'data' exist in your ejs template but not in your node express route.

score 2 · Answer 10 · edited Jun 18 '17 at 19:16

2

For your if statement you need to use typeof:

<% if (typeof user == 'object' && user) { %>

<% } %>

edited Jun 18 '17 at 19:16

eebbesen

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answered Jul 19 '16 at 08:16

Fabien Thetis

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score 2 · Answer 11 · answered Aug 02 '22 at 12:51

2

Update 2022

Use the locals object

This will print the variable if it exists

<%= locals?.yourvariable %>

You can also do

This will run a condition if the variable exists

<% if(locals.yourvariable) { %>
<% } %>

answered Aug 02 '22 at 12:51

Coder Gautam YT

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score 1 · Answer 12 · answered Mar 07 '23 at 10:52

1

Here is the solution you've been looking for:

I just fixed it now.

Code:

<% if(typeof(username)==='undefined') username='Login' %>

Output:

If username exists, then it will be shown as it is. Otherwise username will contain the string 'Login'.

answered Mar 07 '23 at 10:52

Shadman Fatin

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score 0 · Answer 13 · answered Jan 15 '18 at 22:53

I had same issue, and luckily, I found that there is also a short-circuit function in JS (I knew there was one in Ruby and some other languages).

On my server/controller side (this is from Node.js/Express):

return res.render('result', {survey_result : req.session.survey_result&&req.session.survey_result.survey });

See what I did there? The && which follows after a possibly undefined variable (i.e. request.session.survey_result object, which might or might not have form data) is the short-circuit notation in JS. What it does is only evaluate the part that follows the && if the part to the left of the && is NOT undefined. It also does not throw an error when the left part IS undefined. It just ignores it.

Now, in my template (remember that I passed the object req.session.survey_result_survey object to my view as survey_result ) and then I rendered fields as:

<table>
    <tr>
        <td> Name:</td>
        <td> <%=survey_result&&survey_result.name%></td>
    </tr>
    <tr>
        <td> Dojo Location:</td>
        <td> <%=survey_result&&survey_result.dojo_loc%></td>
    </tr>
    <tr>
        <td> Favourite Language:</td>
        <td> <%=survey_result&&survey_result.fave_lang%></td>
    </tr>

I used short-circuit there also, just for safe-keeps.

When I tried it with previously suggested ways, just:

<% if (typeof survey_result !== undefined) { %>
... <!-- some js and/or html code here -->
<% } %>

Sometimes, it would still try to evaluate the properties within the IF statement...Maybe someone can offer an explanation as to why?

Also, I wanted to correct that undefined needs to be without the single quotes, as I saw done in previous examples. Because the condition will never evaluate to true, as you are comparing a String value 'undefined' with a datatype undefined.

score 0 · Answer 14 · answered Dec 22 '19 at 18:30

0

You can use this trick :

user.name // stops code execution,if user is undefined
(scope.user||0).name // === undefined

where scope is parent object of user

answered Dec 22 '19 at 18:30

Alex Szücs

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score 0 · Answer 15 · answered Jan 07 '20 at 19:55

if you plan to use the same object often, you could use a function like this:

<% function userObj(obj){
    //replace user with what you name your object
    if(typeof user === 'object'){
        let result = user;
        if(obj){
            obj = obj.split('.');
            for(let i = 0; i < obj.length; i++){
                if(obj[i] && obj[i].trim() !== '' && result[obj[i]]){
                    result = result[obj[i]];
                }else{
                    result = false;
                    break;
                }
            }
        }
        return result;
    }
    return false;
} %>

usage:

<% if(userObj('name')){
    <h2><%= userObj('name') %></h2>
} %>

score 0 · Answer 16 · answered Apr 25 '20 at 18:26

0

I have come up with another solution.

<% if(user){ %>
   <% if(user.name){ %>
     <h1><%= user.name %></h1>
<%}}%>

I hope this helps.

answered Apr 25 '20 at 18:26

plutolaser

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4
17

1

You can join both conditionals in just one evaluation: ``if (user && user.name)`` – Jonathan Brizio Nov 29 '20 at 12:52

score 0 · Answer 17 · answered Feb 14 '22 at 10:56

The safest and only solution that worked for me

<% if (typeof user !== 'undefined' && typeof user.name !== 'undefined') { %>
    <h2><%= user.name %></h2>
<% } %>

Or a short version

<% (typeof user !== 'undefined' && typeof user.name !== 'undefined') ? user.name : '' %>

KrisNew · Answer 18 · 2022-08-03T13:38:37.600

0

I read somewhere using locals isn't perfect so I came up with something like this, for example:

in express file:

const toRender = {
 user: false,
};
//...
if (userExists) {
 toRender.user = true;
 toRender.data = userData;
}
res.render("site", {info: toRender});

and in ejs template:

<% if (info.user) { %>
    <h2><%= info.data.name %></h2>
<% } %>

edited Aug 03 '22 at 13:38

answered Aug 03 '22 at 13:37

KrisNew

1
1

score 0 · Answer 19 · answered Mar 14 '23 at 10:21

I wanted to use one template and conditionally display a bit more data.

I tried <? more_data = more_data ?? false ?>, which is how I prefer to do it in typescript (and other languages that support it). This would fix it in PHP, as php is pretty null-tolerable at set-time, but less so at read-time (works great).

After reading some answers here..

<? more_data = locals.more_data ?? false ?>

score -2 · Answer 20 · edited Feb 06 '21 at 10:39

-2

I found what I believe to be a better solution on Joe Andrieu's blog:

<%= user.name ? user.name : '' %>

This applies in more situations than the other answers (i.e., when you need to check if a single property exists).

edited Feb 06 '21 at 10:39

Cody Gray - on strike

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answered Feb 06 '21 at 05:49

Brett

1

What is the proper way to check for existence of variable in an EJS template (using ExpressJS)?

20 Answers20

Update 2022

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