Handlebars #if and numeric zeroes

Question

In my Handlebars template I check for the existence of a variable, and render some text if it's there:

{{#if foo}}
  some text
{{/if}}

This works fine if foo is text or if foo is numeric but not zero. But if

var foo = 0;

then {{#if foo}} returns false.

This appears to be yet another Javascript oddity, because Javascript itself behaves the same way. In Javascript code, though, you could get around this by checking if the variable is 'undefined'.

How can I do the same thing in Handlebars?

I could write an {{#exists}} helper, but I was hoping there was something built in.

Answer 1

There is something built in for this:

{{#if foo includeZero=true}}
    foo!
{{/if}}

This displays foo! when foo is 0.

Answer 2

I would go one better and provide a case for the {{else}} condition...

/**
 * The {{#exists}} helper checks if a variable is defined.
 */
Handlebars.registerHelper('exists', function(variable, options) {
    if (typeof variable !== 'undefined') {
        return options.fn(this);
    } else {
        return options.inverse(this);
    }
});

Now you can have:

{{#exists myvar}}
  <p>Value of myvar is ... {{myvar}}</p>
{{else}}
  <p>Please supply a myvar</p>
{{/exists}}

Answer 3

I just went ahead and wrote an {{#exists}} helper. But if someone has a better solution, please post it.

/**
 * The {{#exists}} helper checks if a variable is defined.
 */
Handlebars.registerHelper('exists', function(variable, options) {
    if (typeof variable !== 'undefined') {
        return options.fn(this);
    }
});