How would you check for undefined property in ejs for node.js?

Question

What is the best way to check for an undefined property in an ejs template?

(I'm using the node.js package by TJ Holowaychuk)

Example:

var tpl = '<% if (foo) { %>foo defined<% } else { %>foo undefined<% } %>';
console.log(ejs.render(tpl, { locals: { bar: "baz" } }));

I'd expect this to render "foo undefined". It does throw an foo undefined error instead.

I know that this is not supposed to be an issue, since this is expected behavior in the tests. Is there an easy way to avoid this?

The only solution I found is using the hasOwnProperty method.

var tpl = '<% if (hasOwnProperty("foo")) { %>foo defined<% } else { %>foo undefined<% } %>';
console.log(ejs.render(tpl, { locals: { bar: "baz"} }));

This doesn't throw any errors.

Is there a better way to keep the template clean? Or why does it throw this error?

score 77 · Accepted Answer · answered Sep 07 '11 at 14:06

77

Another way to test for a property is to reference it indirectly via the locals object. Using your example:

var tpl = '<% if(locals.foo){ %>foo defined<% }else{ %>foo undefined<% } %>';
console.log(ejs.render(tpl, { locals: { bar: "baz"} }));

answered Sep 07 '11 at 14:06

Richard Marr

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Just what I needed, but wtf, why do you have to do this?! :) – Oscar Godson Oct 14 '13 at 04:50
Not sure without checking the source, but I suspect that the template engine doesn't bother to scope variables for undefined values. – Richard Marr Oct 14 '13 at 06:38

score 33 · Answer 2 · answered Sep 02 '11 at 22:52

33

I would use typeof, as in if (typeof foo == 'undefined'). I use the typeof operator with the string "undefined", whereas some people might do a direct comparison with the undefined global variable. I prefer this method because it is protected against some terrorist JS library developer changing the value of the global variable, leaving your code broken.

This could also be expressed as a ternary, which some view as "cleaner" due to the absence of curlies:

var tpl = '<% (typeof foo != "undefined" ? %>foo defined<% : %>foo undefined<% ) %>';

answered Sep 02 '11 at 22:52

Chris Baker

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This works and maybe it's the formally correct one. But I personally don't like it, since it's too long for my templates. – pvorb Sep 09 '11 at 12:06
1

Note that this is the only method that will work with client side EJS templates. The other methods rely on checking the `res` object which will not exist with client side templates. – dbasch Dec 02 '14 at 19:14

score 16 · Answer 3 · answered Feb 26 '14 at 23:31

16

Simplest, and cleanest in my opinion:

<%= (!!locals.foo)?foo:'' %>

answered Feb 26 '14 at 23:31

rob_james

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locals seems to have moved to the res object in later ejs versions. – dbasch Jun 09 '14 at 18:19
Can confirm that <%= (locals.title) ? title : "Default Title" %> works – jpisty Jul 07 '20 at 10:38

Subhradip D. · Answer 4 · 2020-05-02T23:32:51.987

3

Earlier version of EJS supports only locals But Now in the latest versions of EJS support res.locals

Sample with ternary operator -

<%= (res.locals.foo)?"foo":"" %>

Sample with if-else -

<% if (res.locals.urvariable) { %>
   <h1><%= urvariable.value1 %></h1> 
<% } else { %> 
   <h1><%= urvariable.value2 %></h1> 
<% } %>

edited May 02 '20 at 23:32

answered May 02 '20 at 23:07

Subhradip D.

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How would you check for undefined property in ejs for node.js?

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