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 t         


        

Answer 1

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<% ) %>';

Answer 2

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"} }));

Answer 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> 
<% } %>

Answer 4

Simplest, and cleanest in my opinion:

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